Parry is a defensive ability.
I forgot that, I just pulled him 3 times in titan and want a reason to upgrade him but I can't be less excited about.
Parry can’t fail due to AAR, there’s a synergy that lets him evade…and it helps him on defense if he’s on a node like biohazard or thorns that adds a defensive ability. It’s a niche bonus, not a core part of his kit.
Apart from parries always working (at least against ability accuracy modifications), I think it also protects your dexes. I suspect that Domino can't make your dexes fail due to her -15% ability accuracy ability, for example.