Marvel Heroes and COC came out before the 'cut off' point where Ike ordered that no X-Men and FF characters must appear in future games and media made by Marvel outside the comics, hence why they continue to be allowed to because of licencing issues. Avengers Alliance 2 for example, no X-Men characters or FF characters compared to the first.
Anyway, I'd rather have a Marvel solo game, don't give a damn about Capcom characters who just took up wasted space in those games. Let Capcom make a Capcom solo game if they want. I'm sure it would sell but I wouldn't especially care.