Warriors and rogues had the worst of both worlds. They had moves and abilities that didn't look physically realistic at all or make any in-universe sense (Leliana's songs, anyone?) while also just being slow and clunky. If you're going to have immersion-breakers like those songs and Momentum, might as well make it tighter, more responsive, more fun.
I loved Momentum, actually improved immersion for me. Yeah, you see airstreams coming off them, but it's not a bad abstraction of how actual cqc can seem like a blur with moments where time seems to stop, combining with the slow down finishers, I mean. That's basically my experience in real fights. It's basically like a series of blurs and these flash perception moments where your mind kind of goes into this extreme focus and you're perceiving everything occurring in these little slices of time where you decide how to intercept that and how you're going to execute your next action. And you're operating in this heightened state. Firing on all cylanders. I used to actually enjoy the physical part of it, because it's just this high. Adrenaline high. That's how it really is in my experience.
That's what "the zone" is really describing too, in sports for example. For instance, I played baseball as a kid (not really my favorite sport, prefer hoops, but I liked playing), and at one point this guy hit a line drive straight into my teeth and layed me out. The next time that happened, same scenario, it seemed like time stopped with the baseball sitting right there in front of my face, and I had time to swing my glove up and snag it out of the air. Because that focus kicked in.
So that whole flow between momentum boosted combat and finishers was probably the most immersive thing about DA:O combat to me. Plus it has the effect of just speeding up combat and improving efficiency, so it's great imo.