Balancing... because it's a hot topic right now
Forewarning... 1. while I have some specific ideas of changes I feel should be made (or options), I will try to withhold these except perhaps as an example to clarify 2. this will probably become tl;dr
Balancing champions/items/game is a hot topic these days. And it is my belief that there's been a lot of bad attempts (or simply lack of attempting at all) in recent history, and a few good ones. So I will endeavor to offer a better system to employ when thinking about balancing. It doesn't offer an immediate "fix"/band-aid like what's currently being employed. It isn't something that can be done in one patch. It may not even be 100% doable, but it can serve as a guiding philosophy which will lead to much better long-term balance and make future balancing much easier.
Premise 1. balance champs around each other in a vacuum. No items or runes to consider... just the champs, their base stats and abilities throughout the game. Why? If you do this... you have a firm foundation to begin with. You don't build a tower without creating a solid foundation/base. If you do, you are asking for any little mistake further on to topple the whole thing. Balancing champions around each other is the best point to focus when creating that solid base in league.
What does it look like? There's 2 points of focus in this regard that I've come up with. A. A champion's power curve. Some champs are moderately strong throughout the game, but never S class so to speak. A classic example throughout most of league's history would be orianna. She's solid in lane, but not top tier. She's solid mid game, but there's others with more midgame power. She's great late game, but there are still mids stronger than her late game. Other champs are very strong early and fall off hard. Still more scale up to be nigh unbeatable late game, but have weaker early/mid games. And there's other oddballs that have different power curves still. Power curves are not properly balanced currently and furthermore are being balanced around items. This is a bigger problem than you think because issues arising from an item now create more problems due to unnecessary over-linking of them to a champion's power such that 2 problems must be fixed in order to fix the itemization problem: itemization, connected champion(s). Which can in turn create more problems with both or with runes. And thus we see the need to balance champions apart from itemization such that when itemization problems arise, we can adjust the items and not have to worry nearly so much about champions. Items will be designed with the balance of champions in mind... not the other way around and any items being far too strong on a particular group of champions will simply be removed or reworked so that they don't over-empower said champs. Which is possible to do because... we have our firm foundation of balanced champs to know the problem is not with the champs themselves but rather with the items.
B. The triumvirate. Damage (burst, dps), durability (innate stats, resists, and itemization multipliers within champ kits - think malph and armor), and mobility. These three things must be accounted for when designing and balancing champions. The better mobility I have and the more dps... the lower my durability should be if I actually get hit by an enemy. Conversely, the higher my durability and damage (hi mundo as a hot-topic current example), the lower my mobility should be. Now, like power curves, we can have different combo's of these and they can even be designed to change throughout the game. Like I might be a 4/10 on two of these and a 7/10 on the third. Or I might be strong in damage early, but fall off in damage in exchange for mobility and durability later into the game.
Premise 2. balance items around champions. There's been some good attempts and/or fixes in this regards. Recognizing stuff like... oh lethality is too strong... let's do this to fix it. Or a lot of other roles are buying and abusing gp5/gp10 support items to increase gold income... let's change this to stop the abuse. Anyways, items should generally be designed with champion roles in mind... which they largely are. This could be map position (support, mid, adc, etc.) and/or class (bruiser, mage, assassin, etc.). But then their potential interaction(s) with other classes needs to be considered before shipping to live. Could another class completely abuse this? Does it synergize too well with another item(s)? Does it essentially merely provide a duplicate to another item already in the game? Is this going to be completely broken based on a certain champ(s)'s kit? Since we know champs are balanced among themselves... any issues with the item mean it synergizes too well with a champ or set of champs and can be adjusted with that in mind... rather than adjusting the champs and throwing off the balance of... everything.
This should be done in a way that promotes multiple potential builds which can be viable in the right scenario rather than one standard build to which all others are inferior. Ex: an adc might buy maw instead of last whisper item one game, and might sub out ga for bloodthirster another. It depends on their opponent's team comp and their own team comp as well as how that specific match is going. This is the whole point of having items. Unlike HOTS, LOL offers itemization to increase a player's ability to create the champ they want. Now, that doesn't mean every single item needs to be viable on every champ or that champs should be adjusted just to do something like making ap renekton actually viable. You designed the champs with a goal/purpose in mind. They are designed to fulfill that role and that's it. If someone wants ap renekton to be stronger, you don't go changing itemization just to make it viable... because that would break those items for a ton of other champs. Make sense?
Premise 3. finally a short one. Runes should be balanced in much the same way as items are in premise 2.
Employing a strategy like this to get it even remotely close to reality will require massive time investment. Likely more than one season. It must begin with champions themselves using both power curves and the triumvirate. This provides the solid foundation which enables much simpler balancing of the rest of the game (items, runes). Once you have this foundation, it is also then more possible to properly balance new champs because you can simply compare them to other champs. Any items which make them broken mean... adjusting the item(s) rather than gutting or over-buffing the champ to make it viable only to realize that it's broken if a different built is employed/discovered. While it is a HUGE initial investment, attacking the issue of balance with a framework like this in mind will lead to less stress and better long-term solutions (as opposed to band-aids) in the future.
The speed of the game can also be tuned more by itemization and runes too... to increase/decrease average game time. This is important because along with new items and champions, this keeps the game fresh... without breaking it. What do I exactly mean by this? Well, let's take a theoretical example. So the game is properly balanced, renekton is once again super strong early and a proper lane bully who falls off by a proper amount late. Jax is properly weak early in exchange for his amazing dueling power late. So if the game time averages 35+ minutes and is favoring jax winning, that's ok... because it's due to average game length. Wait a second... I'm the renekton player here... why is this ok? Glad you asked. You see... that's average game time. The game is properly balanced, items properly balanced, runes balanced, etc. So, while average game time means jax can typically get to his items and win out late... we still have the early game bully potential and everything properly balanced to give us the fair chance to wreck him in lane and end quickly. So... we can 100% win if we play properly without having to massively outplay him to stand any chance of winning. Change around some runes, items, etc. a bit but still keep them balanced properly among champs and we have a new meta/patch where game time averages 25 min. Now games aren't typically lasting long enough to let jax get enough items to outscale us on renekton. But... jax plays properly and he can still stall out the game or get a lead in lane through outplay and/or teamwork and get the lead he needs to carry. Jax can still win because the champs, items, runes are balanced. It might not happen as often... because of the meta we are in and the average game time. This doesn't mean jax or renekton or items are imbalanced... it simply means that the current average game time favors my champ due to him having a stronger power curve during this timeframe of the game. Just as jax having higher win percentage in 35 min gametime meta doesn't mean he's broken; it just means his power curve is better when the game lasts that long. Does that make sense? Neither side is not given a fair chance to win and both sides are aware of the risks with their picks in either meta and still given a fair shake at winning. *it should be noted with this that extremely lopsided power curves... like crit adc's right now... should be avoided. They introduce too little power at one point of the game to have the champ be relevant in exchange for too much power at another point to make it unfair to play against them. Thus, if power curve ratings were looked at on a scale of 1-10 for each point in the game for a champion, they should stay 3-8... not drift into the 1-2 or 9-10 range at any point in the game. Both because that makes it far too punishing for them during their weakest phase and because it makes it far too punishing for their opponent(s) during their strongest phase. This doesn't allow for them to properly survive their weak phase early or be relevant past a certain point of the game (regardless of how well they play) if their late game is that weak. Likewise, it offers their opponents no counter-play other than... literally don't be on the same screen as them unless you have 1-2 teammates with you during their strong phase. Hopefully that makes sense. The way I see it... you have about half a split left to use a framework like this... and the whole offseason to start utilizing this to look at balancing the game long-term. I expect you could have champs fairly balanced by next season of ranked (not pre-season, but start of season) via this type of framework. Items and runes might take much of the spring split to get balanced along with finishing touches to champion balance. Because this would feel pretty aweful if implemented in stages and totally out of whack for balance, I believe the best bet would be keeping a temp balance team to handle things like they are now... from patch to patch and a separate team to investigate balance via this type of framework... but not implement any changes to live or even pbe until they've established the "solid base" of a balanced champion roster. Then as that has been accomplished, introduce the properly balanced champions into pbe or something and start gathering data and feedback from internal testers, pbe, and high elo players and pro's. Utilize this to begin itemization and rune balancing. So realistically, the results of balancing via this type of framework would not be seen by the community until probably at least next summer split. And there would still be bits and pieces being worked on then, but it would be in a much better state than most people view the game today and only improve from there. Anyways, that's my idea for how to better go about balancing the game. Hopefully you can take at least some of these ideas to heart and start utilizing them to improve the game in a way that the majority of players will appreciate and enjoy.