To me, the biggest mistake Riot made was removing the old runes/masteries, then adding keystones

And this highlights arguably Riot’s worst flaw as a company regarding balance, which I’ll address in a moment.

The original runes and mastery system was completely fine. Riot’s argument against it was that it didn’t feel impactful and it was bland, both of which honestly weren’t true. Try playing the game without runes or masteries on a new account or forgetting to save mastery changes and going in 0/0/0. They were definitely impactful, they simply didn’t break the game to ridiculous levels like keystones did.

This idea that they were bland was inaccurate as well. You know why Pantheon became a menace? Thunderlords and the inability to stack armor early. I used to run a total armor rune page, + cloth 5 and/or flask + potions. This actually gave you the ability to pick different options for out-sustaining bullies. Now, when everyone goes corrupting potion and you take any damage keystone, outsustaining isn’t an option, plus the additional damage from the keystone where damage like this never existed before in the early game (practically gave you an additional spell) and corruption burn damage. Obviously the keystones have changed this season, as have the items but it’s all still the same more or less.

Old runes and masteries were impactful but only subtly so. It wasn’t obnoxiously overpowered and it didn’t power creep the game. Sure, most setups were generic and the same thing but how is that really any different now? You merely replace a proven system that had years of repetitive success with a new, more broken and a much more impactful system that has contributed to the power creeping of this game and the absurd amount of damage output we have now, mostly because of keystones. This has single handily ruined the gameplay for most tanks and weak early game champions because baring a few exceptions, the keystones that have been the most broken and constant all reward and amplify damage while any sign or scent of a true defensive keystone simply doesn’t exist. And please, for the love of god, don’t create it.

It’s ironic, too. The old mastery system was way more diverse than this crap now. Anyone from season 3 remembers how many different setups you could have. 21/9/0, 21/0/9, 9/21/0, 0/21/9, 9/0/21 and 0/9/21 were all totally viable options that enabled a unique play style or variation of one for many champions. Anyone remember 9/0/21 perma kite vlad? Yeah his damage was weaker but that was the trade off you made for more spell vamp and movement speed. You could go 21/9 or 21/0/9 if you wanted more burst and sustained damage and you could go 9/21/0 for more tackiness in the early game. The realty is, that doesn’t exist now, or maybe it does but we haven’t yet found it out because you’ll just massively overhaul it again. Even if the former isn’t true, the ladder is and vice versa (I suspect the former is true though).

And that speaks, to what I believe, is Riot’s biggest flaw as a company. Too many times, they have changed things that were totally fine just for the sake of changing. What’s the old saying? If it ain’t broke, don’t fix it. Yet, a system that ran successfully for 5+ years suddenly had to go just for the sake of satisfying someone’s curiosity most likely. There was hardly an outcry to overhaul the rune and mastery system. By season 5, you guys just made it so bland because you nerfed just about all the different rune/mastery setups or randomly changed them to be more bland when in reality, while they certainly broke the game at times, they were hardly a huge problem in the grand scheme of things. Sometimes simplicity and longevity is best, you don’t have to change everything to keep things fresh: plenty of things change in this game, it was nice that something remained so static over the years that allowed people to feel coming back to this game from a few months off didn’t require such an investment in time now. And now, it’s gotten to a point where even Riot really doesn’t have the resources or wisdom to balance this hideously broken game. The ultimate irony.

In my opinion, you should just scrap keystones and go back to the old runes/mastery system and keep the noob trap runes out of the game while allowing runes to be free and accessible at every summoner level, same for masteries. I actually believe that alone would fix so many problems. Of course, you still need to get rid of baron insta dying, towers melting so quickly, cheap damage items and a few other things that remove strategic gameplay, but hey, this would be a good start.