A good parry mechanic is a kind of redemption. Where blocking - aka holding a button to avoid damage - is a concession to the tedious attritional undertow of many action games, parrying - aka pressing a button on cue to cancel damage and often, prep a counter - is the act of cutting through the bullshit. It passively reduces any and all visual and thematic overwhelm the game would have you experience to a question of timing.
In the face of a good parry mechanic, the grandest of bosses are equivalent to rank-and-file mobs. You're a monster the size of a building? You're the demonic manifestation of a protagonist's mother issues? You're capitalism incarnate? You're wielding eight chainsaws at once? Ehhh. I'm not just going to survive your onslaught. I'm going to dismiss it. All of it: your absurd DPS, your multiple elemental modifiers, your screen-blanketing special effects, your overcooked core concept, the very laws of physics - poof, gone, as though they had never been. Blocking is akin to maintaining a poker face while you're being harangued by your boss over Zoom. Parrying is politely pointing out that your boss has left his camera on, and that he should probably wear trousers when he's at work. It is "nope" said so quietly that it shuts everything else up.