How to fix this game from the ground up: delete literally half of it
I know at first this sounds like an ironic take on some boards threads that say "delete this", or "delete that", but this is supposed to be a serious thread. I think it is obvious that the current issues and problems run too deep in the game to be easily fixed by mere number juggling on a superficial level, and you know why? Because there are too many systems in place that somehow DO MORE HARM THAN THEY DO GOOD.
So let's start with the deletion list that for some reason does not include a single champion!
1.) The entire Rune/Mastery-business in general.
You see, back in the day we had this thing for "playstyle customization". However, in a game with like a 150 champs, IS THAT STILL NECESSARY? If you don't like the playstyle of one champion, go play another, it's not like we don't have one massive varaiety to choose from. I could have seen the necessity in the early stages when we had like a 40 champs for 4-5 roles, but today? Not really needed, especially with all the problems the mere existence of such a system causes.
For balancing, such out-of-the-game systems are a nightmare. Every single champion needs to be balanced so they are not op with any combination of runes and masteries they run. However, now also every champion needs to be balanced so they are not completly useless when they are not playing with their "best setup". And overall: such a system just pushes even more damage, because as it is the nature of the genre, the offensive options will always be of more use than the defensive ones.
You know how to balance a highly complex game? First of all you cut down the complexity! And Runes and Masteries themselves got nothing to do with the ACTUAL GAMEPLAY. In fact, they distract from it! This game is about awesome champions doing awesome things, yet somehow a whole lot of the power the player uses does come from some random rune setup that's not in any way connected to them. That's bad design if you ask me.
Generally the whole thing just feels so forced. Like "we had a system like this in the past, now we need to have it too" - which in general is a very shitty reason to do things, if it's the only reason, which it undoubtingly is - after all, I explained above how the "playstyle customization"-argument just does not work anymore.
2.) Every single item in the game, then redo it from the base up.
Another thing that falls under the "power from outside a champions kit" category: items. However, I don't want to go full HotS here and throw them out, because they DO have a function in defining how individual progress in a single match works. But... we really need to look at them from the base. Why does a Ruby Crystal cost 400 gold? Why does it give as much HP as it gives? How much gold is every point of stat supposed to cost? What can a laner buy after getting an early kill? And what not? How many farmed minions does this item require?
This allows us to finally create new items with actual freedom in design: we wouldn't have to worry about how a new item fits into current itemization choices of certain classes, when we re-design all the items. This also leads us to point 3:
3.) Ancient remnants of the game's early stages
Grivious Wounds. Random Crit. Lifesteal... all these things existed in the WC3 engine that the original DotA was made in, and that would be the basis for this game, yet they all do more harm than good: Grivious Wounds make balancing healer-champions really wonky, crit was originally brought in to make ADCs buy a stat that would not immedeatly make them shred towers, but those crumble like wet paper anyways and it leads to horrible gameplay with victory decided by chance and not by skill, and lifesteal... you know, sticking sustain to champions that should definetly not have it by class definition is surely not really a good idea, and playing around lifesteal usually results in "just kill them as hard as you can", because predicting how much they are going to heal per hit, especially with crit variance, is just such an annoyance none's really going to bother with.
I mean we kicked out dodge (for good reasons - I doubt most players reading this will even REMEMBER dodge, that's how ancient it was, and those who do will do so with dread), so why not do it with the rest of these stats? Like this, a lot of design-space that was cluttered before has been freed up for more interesting unqiue items.
Seriously a lot of the problems in the game seem to come from everything being build and and expanded from a wonky basis, and somehow trying to change something on such a fundamental level was considered heresy. But we should keep in mind: league was never a perfect game, and even if for the most years we thought of it as "heading in the right direction" (which it mostly did save for the Ghostcrawler era heralded by the juggenauts which HOPEFULLY has come to an end now), it had fundamental flaws and irritating quirks that need to be worked on.
Or to make it short: instead of trying to fix a hopelessly broken house, it might be cheaper, faster, and more satisfying for everyone to tear it down, fix the fundamentals, and then build it completly new.