I have zero problem with reusing assets if it allows the game to be bigger and better than it would have been with out it. That is actually the problem with the games roster because they reused so many assets that you would think that it would make the roster much bigger than it seems to be. That is one of the indicators that this game either had a small budget or was rushed.
That has always been the issue when we see sequels for fighting games. When you have a fighting game that basically has too many returning characters, you make people wonder why a new game was being made while if you put in too many new characters while alienating the old cast, you have people feeling uneasy about the sudden change in the roster. You need to strike that sweet spot where there is that nice balance of old and new, otherwise you run into the issue of angering one of the two camps.
In this case, the idea for MvC: Infinite having so little new characters is making some people think that the roster is basically a water down of the UMvC3 cast with a few characters being replaced for others and calling it "New" even though they are still their own characters. Only other problem is that alongside with the small set of "new characters" that we are going to see, other brand characters that will be added in as DLC.
If we were to just look at the brand new additions to the initial roster, the game itself feels underwhelming. It is nice that we have five new characters, but that is five characters out of a roster that is currently at 27 (and again, this is not counting the DLC characters that have been confirmed or are on the way).
