Saying that Envi cleared floor 12 "by abusing reactions" is extremely oversimplified.
He cleared it by learning damn near every attack pattern over hundreds (thousands?) of attempts. His best damage dealer was actually Xiangling doing physical damage because lolCrescentPike.
Yeah, of course reactions are important, the game shoves them in your face most of the time. That doesn't mean the game can't be heavily built on more than one mechanic. Arguing that somehow dodging isn't a core gameplay mechanic just because reactions exist is like saying tanking isn't a core role in WoW because healing exists.
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Well, you can do Childe without taking any damage, it just requires a lot of knowledge of his patterns and patience.
Usually I'm not that patient so I take a lot of damage in the tradeoff, what can I say.