Just making it faster isn't going to address those issues.
I think it just needs a different concept-- the after-image shtick works with Sword-based crits for several reasons, but with a Bow those don't really apply and it just ends up impractical and... kind of silly? Even under Rule of Cool.
Let's take a step back and look at the a couple of the other GBA crits.
In the case of Swordmasters, instead of their typical forward leap... they backflip! And then they're suddenly everywhere but forward, and just as suddenly they're completely gone! But then whooshy whooshy whish and peek-a-boo! they're up in front of their target after all and it's over before they even know what hit them. It's ridiculous, cliché, and over-the-top flashy, but all the fake-outs are so thoughtfully placed and well-done that the animation is still compelling every single time. And more importantly, even as something inherently physically impossible, it intuitively makes sense.
An Archer's normal animation is 3 simple steps-- draw an arrow, aim, shoot. Not much to it, so how do you crank that to 11 for a crit? Nock multiple arrows at once? No, that's a lazy way out and from the looks of it they've only got the single projectile animation to work with anyways. Do you make them backflip or do something crazy? No, leave that to the agile melee classes. But then how can archers look cool? By playing to what makes them cool, of course: one shot one kill. When you'd normally expect them to casually draw an arrow, they pause to focus for a single, heavy moment and that's all you need to build up suspense in that split second and feel like ohhhhhhhh it's about to go down. And then the casually effortless spin, and POW! dead. drdrdrdrdrDING! Level up. Eat your heart out, Legolas.
Now look at Warriors with Bows: there's no finesse about them, and they don't need any buildup either. Right out of the gate they're instantly taking total command of their enormous weapon as if it was weightless and firing off a powerful shot in one fluid motion. The sense of overwhelming power is conveyed bluntly and decisively, just like you'd expect from that class.
So. Assassins. What is this class's identity, how do they fight? They're not Swordmasters, but they're nearly as fast. And they don't fight head-to-head, in fact they don't want to fight-- Assassins strike to end it before there's a fight at all. Like the Thief's swaying lure, making you uncertain where they'll-- oh sht he has a knife!? Except where a Thief gives off the vibe of doing it because they have to, an Assassin should do it because they *can.
The Assassin's own sword animation