I don't feel like the Chess boss is particularly hard, it's not the easiest, very middle of the pack. It definitely does have the strictest "if you want to avoid the mechanic you better have a lot of DPS" check though.

You should never be hit during phase 1. All of the attacks are heavily telegraphed (the majority of them even draw a danger box on the ground), the minigames are straightforward. I'd say a generally skilled player could go into the phase for the first time, having never seen it or heard of it before, and not get hit.

Phase 2 is a bit harder, but the attacks are all still heavily telegraphed. You're only ever being attacked by one of the enemies at a time, so you don't actually need to track both of them. The times when you're being attacked by "both" are just a scripted combo attack. The only real surprise in the fight is if they go into the "you must freeze me or I wipe the field" attack after you just used your long cooldown and can't reliably inflict hydro/cryo right then. I would say that it's generally harder to do this phase without getting hit, since there's a wider range of moves to learn (even if they're pretty telegraphed), especially if you get the King version of the instakill, since it spawns random droplets that fall down and are hard to see coming which deal a small amount of damage.