Yeah, there's no reason to redo something like a 3D animation if it works in your engine and doesn't look janky/outdated. We know what it looks like when Heihachi kicks, no need to reinvent the wheel.
Really, I don't think there's anything wrong with reusing assets in fighting games. It's been done since forever. The problem with MvC:I is that we aren't seeing the usual benefits of reusing assets (larger rosters) and some people aren't happy with who was reused, like Arthur, Firebrand, or Nemesis.
The latter is subjective, of course. I'm super happy to see Nemesis again.
I also think Marvel's side of the roster is just fine, providing you accept that it's MCU-focused. I made peace with that at the game's announcement.