Actually, Marvel vs. Capcom 3 does have infinite combos and not hard to find.
The Akuma and Captain America infinites were taken out. Captain America was considered a pretty low tier character even *with* his infinite. Infinite combos are literally a non-issue in this game, since it's relatively easy to 100% combo in this game without infinites, if there even are any left in the game. I can't remember if the Deadpool bolo loop lets you go further than like 12 reps or not.
As for balance, apparently you do not know as much as you think you do. Capcom even had to patch the game a month after release to fix some balance issues (one of the changes was Sentinel having his health reduced by 31%).
Part of the reason why Sentinel is no longer considered top, but it wasn't really a super big change since it didn't change his ridiculous damage output. Also, I can't believe neither of you guys have brought up Wolverine yet, the actual best character right now.
Oh, and another thing: SF4, SSF4 and MK9 also had patches out the first month, MVC3 isn't special in this regard. And it's also not like the game was broken for Sentinel having 1.25 million health, he still had unfavorable matchups with a number of the other characters.
And just because you play in tournaments doesn't mean you know the game inside and out, many tournaments are open to anyone who wants to play.
Maybe I should have mentioned that I've won most tournaments in my state, placed 2nd in the ones I didn't win, and that I have taken matches off of Viscant. Do you know who that is?