Let's hold off on the celebration of masteries damage amp nerfs for a sec
Note to reader: this is a long read, very basic tl;dr summary at the bottom.
I understand everyone is frustrated with "damage creep" but do we even have demonstrative proof that it exists? No, seriously, look at itemization now understand that most offensive values of now are down compared to where they used to be across the board. It's harder for ADCs to get a lot of crit so they have to pick between AS/AD/armor pen, I would be willing to bet ADC overall damage is slightly down if not roughly the same. AP damage is definitely down, you basically cap out around 700AP now unless you're veigar. Bruisers damage is roughly the same in their itemization whereas AD caster itemization is currently overturned as heck.
I'm speculating here, I don't have definitive proof that my claims are true. And to be totally honest, it would be a lot of work to even prove this because you'd basically have to take all the champions in the game of now and compare them to their selves in seasons pasts with old itemization, etc - it'd be very messy to do. So I'm not asking you to cherry pick examples that prove me right or wrong because I actually suspect damage in terms of itemization is probably around the same, if not slightly weaker than it was in older seasons.
Here's where I think a case can be made for more absurd damage output: all the damage amps in masteries and keystones. And I realize that maybe this is the problem but I'm not so sure nerfing them across the board is a good idea. You are objectively making 1/3rd of the stats you get in the utility tree (offense, defense and utility) significantly weaker. That sounds great on paper, but just remember one will likely become much stronger as a result - which is likely defense. Then what? Do we need defense until we end up going back and nerfing offense again or utility when they become dominate? This is the never ending fruitless balance cycle you have with champions and you can't avoid that. Their kits have too many complexities, their synergies with items and other champions adds too many variables to accurately predict and balance. And that's why it's okay for this process to be used ok champions.
You know what you didn't need to use this for? The old masteries. The older masteries were bland and very straight forward and while they did add significant power, it wasn't typically until the bottom of the tree and you'd have to sacrifice a lot to get it. Now, the focus on the bottom has become so great because of keystones, and keystones are so powerful, that they constantly get nerfed and the balance of masteries is in a never ending cycle of balance that wasn't necessary in the first place because the old mastery system was fine. you didn't need to change it and it was a stupid idea to change it in the first place because look what disaster you're left with now. Eventually these masteries will be so watered down because they've all been so nerfed that they'll fill like total shit anyway, even weaker than the old masteries. And that's what makes keystones and the concept of this complex mastery system so damn aggravating because you added another complex variable to the game to balance since keystones have various impacts on all the champions across the board.
Sometimes simple is better. Sometimes you go to far and you end up overstepping and making things worse. The old mastery system was generic but it needed to be because we see what a cluster fuck of balance these keystone masteries have caused. Tanks doing obscene damage through obscene healing, literally bruiser everything being possible because fervor, random 5th spell added to everyone's kit for doing 3 things, obscene random lifesteal, random dot damage that can never be balanced because dots are so stupid and uninteractive, random absurdly increased shielding and heals, random insanely increased damage reduction, random health. Like seriously, every keystone has been broken at one point or another except stormraiders. And I don't think the direction should be to make more masteries like stormraiders because you've shown in two years you aren't capable of it, probably because making 8 other keystones that balanced while that potential of strength is impossible. You can't keep buffing/nerfing because keystones have a profound impact on the game. You're just going to swap one broken set for another and I've already explained that mess.
Tl;dr go back to the old mastery system next season. Keystones and this mastery tree system were a nice expirement but they don't work.