1 thing that makes NO sense what-so-ever (assassins)

Try hitting Right Bumper(DashNSlash) right before or after grappling or both . Works for me quite a bit.

The other classes also have grapples that function as well in the front. A couple of them have knockback and most have comparable damage.

The extra conditions on the Assassin's grapple mandates the need for stealth abilities, and has limited reward. On top of which, the other classes have other attacks to rely on in a pinch. Like, say, their own powerful grapples, ones that can actually cause a ring out, clear massive distance, or set you up for a shotgun burst you can't avoid. Or their own area of effect attack.