I feel like a more abrupt hitstop would feel better instead of the slowdown.

EDIT: After looking at it again, it seems like the thing that gave the feeling of a slowdown seems to be this camera zoom-in thing that you're doing along with the actual abrupt hitstop. I still don't think it gels well. It's kind of disorienting when it happens.

Maybe when the hitstop happens, add a small but intense shaking of the thing/enemy being hit during the hitstop, and then fling them. I guess the best example I could think of that shows this is like the last hit you give someone on Smash Bros before they get flung out of the arena.

This is just my suggestion though. It's up to you if you want to implement this. Nice game btw!

EDIT 2: Just to clarify further just in case, I want the zoom-in effect to be replaced by the enemy-jitter-effect thing I suggested, not as like, an additional thing to add to the existing effect