The main difference from a traditional parry is that a parry catches an attack after it's released, while an interrupt stops the attack at the moment it begins, preventing it from happening in the first place.
Got it! Thanks for explaining. The video in the corner helped a ton to describe what you're going for. There definitely could be something here. To me it's still parry-focused gameplay, but there could be something unique here if every level the character's progression gets set back to zero and you have to parry enemies to rebuild your stats. This could potentially be a roguelike with multiple levels and various abilities you could collect. Otherwise I'd have a hard time imagining how the stat increase wouldn't break the game pretty quickly with enemy parries.
On the parry timing: for beta testing the idea, I think it's fine for the parries to be easy just to validate if the concept works. But for the final, if it's part of the main mechanic you'll want the window to perhaps be a little tighter. It depends on how impactful the bonuses from landing parries will be. In Sekiro, for instance, the parry doesn't immediately provide benefit only until you stack up enough parries to get a deathblow. Perhaps that's the way this could work where you'll need a certain amount of parries to gain a skill? Just a thought! Best of luck with this.