It has nothing to do with ADCs:

The issue is not ADC burst. Or anything of the kind.

The issue is that everyone is doing way too much damage. Everyone but dedicated enchanters.

It's not just the few exceptions or oddities, even. It's not just Cho'gath and Malphite one-shotting squishies of the tanks. It's not just a few assassins. It's not just the Lux and Karma support, or the lethality MF and Jhin ADC, or any one group. It's everyone except the champions that have historically had no damage (Pretty much most enchanters and Ashe) that's doing insane damage. And, even then, their damage has had the same relative spike (Increased by the same multiplier). They went from way too little damage to average damage.

Part of the problem is that everyone's completely polarized. Honestly, unless you have a lot of innate defense in your kit, an armor and an MR item won't do jack shit for you. A lot of it would be fixed if you could opt into an armor and MR item on everyone. But it just does so little to help you against everyone else that's building straight armor and MR that only , , , and do anything for squishies. And all of these? Only because of their passives/actives (Granted, DD is only a defensive item of any kind because of it's passive, but, still...). Maw of Malmorticus feels...crappy. Not just a meh upgrade to Hexdrinker, only gotten for better slot efficiency as a 5th item, but...it feels legitimately worthless. The shield might give me an extra hit I can take. But most of the time it doesn't.

And then, on the other end, are the serious tanks. The ones that are basically unkillable. But they also seem to have too much damage. Then again, I suspect that's more because we can't afford to get defensive items. does way too much damage, but if I could actually afford the gold or slot to buy a MR item against her, she most likely wouldn't.

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Now, I'll be honest: I have no idea how to fix this. At all. I legitimately have no idea. My only idea so far has been to take 5% damage away from everyone (either by increasing defenses or reducing numbers). Just have everyone do 5% less damage, with the exception of early game basic attacks (because we don't want to completely fuck up farming). I hope that'll help reduce the polarization, because it'd allow you to last a bit longer, meaning armor and MR might be more impactful for squishies...

Or, you could just buff the armor and mr on the squishy defensive items. That might also work.

tl;dr: It's not any one class dealing too much damage. Everyone in the entire game is dealing too much damage for who they are. And that's causing most of the issues.