It's just basic logic. Consider a character like Dormammu. If you remove assists from MvC3, Dormammu would have 9-1 matchups against the majority of the cast. There's just nothing they can do about the combination of his mobility, Flame Carpet, and incredible zoning tools.
Therefore, in a game without assists, a character like Dormammu cannot be allowed to exist. Characters will be forced to be toned down so that everyone can compete on roughly equal grounds. Just look at TvC, which still had assists, but it eliminated tridashes, and see how much that changes the flavor of the game. I'm honestly very worried that tridashes will be gone or toned down in MvCi because tridash characters have incredible advantages over non-tridash characters in the neutral, and since there are no assists in this game, the point character is your neutral.
MvC3 has higher character power levels than any other fighting game on the market, and it can do so BECAUSE of the assists shoring up weaknesses in characters. The next highest is probably Persona 4 Arena, BlazBlue, or Guilty Gear, and not a single character in any of those games could handle Dormammu 1v1.
The gems are just a pointless tacked-on feature that add nothing interesting to the game. So in that sense, they are a lot like SFxT gems!
Nothing would make me happier at this point than to wake up and see that the articles misunderstood Ono, and they meant to write that you'll only have 1 assist.
Feel free to quote me in a year. If I'm wrong, I'm perfectly fine with having my nose rubbed in it.