every time i try to perfectly time a parry against projectiles or possible moves from my opponent, the game skips many frames where i should've been actionable, and i get hit or i just get an imperfect block.  

It's weird. If it's related to some sort of intended mechanic, this should be specified. I had this happen to me once. Not optimal lol.

Maybe wait is always a set number of frames. I'm not sure tbh. I have similar issues with wait. I always just use hold to wait instead. That usually works better. That's what you do in hitstun anyways.

Im not an expert at the game (obviously) but it believe the wait times go until somebody is able to move making the wait times dynamically based rather than static

Edit: I think the timer between moves works like this so you cant parry perfectly all the time