does anyone else feel like NIN's slashes arent very satisfying?

Certainly, finishing off a big boss with an SA does feel nice.

Shadow Fang and Dancing Edge are quite cool too.

Have you ever killed an enemy with a Shadow Fang while pulling away from it? it looks badass, and if not enough to end it, it is even more so if you cast a Shuriken -> Dagger Throw afterwards to finish it off.

They are supposed to be light on their feet and quick, so I think the current animations have about the right weight to them.