About the Sentinel nerf, there one thing I haven't seen anyone mention yet. Wouldn't Capcom have access to an online matchup list? As in Team Akuma/Ameteratsu/Arthur defeats Team Wolverine/X-23/Zero this many percent of the time, most likely with the average remaining HP on each character and whether or not X-Factor had been used. Of course, this would exist for every single combination and individual characters. So if Sentinel had an abnormal win rate AND he had about 400,000 HP remaining in the same amount of wins that he was above the mean, then the reasons behind the nerf become very easy to see. Now with the time a patch takes to get through, this would probably only be based on the first week of online play, where Sentinel pretty much did rule supreme, so it makes sense. He would stick out like a sore thumb in win percentage then.
And, really, why shouldn't Capcom keep track of the online matchups? It's one of the fastest ways to get matchup information for the widest selection of your players. Of course, this would mean that MvC3 would be balanced towards online play, for good and ill.