The excuse that they cannot touch the animations because of some decades-long legacy is nonsense. Frame counts and animations are adjusted in every single minor iteration, let alone major title releases. The changes to timings and balance are the entire point; frame changes are what hardcore fans jump to in changelists.
Namco is also obviously not totally averse to updating dated animations: Tekken 6 cleaned up Law's movelist quite a bit, for example. The modernizations have not been anywhere near evenly distributed, however, and for a 2015 game there is simply no reason for Kazuya's pelvis to still detach from his spine when he performs hellsweeps, or for Heihachi to hover slowly into the air during a powerbomb. Of the major fighter franchises, Tekken is particularly littered with awkward legacy animations.