Thinking outside the box, the most appealing thing about 2h when picking a favorite class in Warband, besides the obvious fluidity in motions, was the over the top and obviously advantageous broken stab mechanic. Hell, it's the class I played the most in both native and SP, for those specific reasons. Everyone loves to be OP and role-play helicopter pad motion Super-man diver.
The animation itself is as if the human model tried to stab something in front of him, and tripped over his untied shoelaces, performing an unthinkable superman motion, and most likely the dev team ran out of funds to redo it back then, so "fuck it, stays like this anyway, we already left so many other things half-arsed anyway".
Senni's animation isn't perfect, obviously, being one of the biggest problems in my opinion, aiming the stab, since the model blocks most of the motion (assuming 3rd person).
So, ultimately, you have all 2h try-hard raging about this for ages, cause you took them the ability of transcending into MLG dorito eating sentient beings while having an unfair advantage mechanic-wise over the rest of the playerbase. A bit like polearm stabs pre-turn-nerf (that pike around everything, good lawd).
If you revert it, you'll most likely have to revert/balance most of polearm stab related stuff.