Here are some characters that are as frequent or moreso than the characters you listed:
Morrigan
Haggar
Sentinel
Hulk
Dormammu
Amaterasu
Strider
Dante
Viper
Approaching a third of the cast, and this is not including character specialists that we see frequently and frequently placing high.
yes, Haggar and Sentinel are both overused assists dunno how I forgot em
Hulk I might give you
Only Dormammu that pops in my head is Champ's
Amaterasu is not used like that. Maybe in vanilla Marvel but not in UMVC3
Strider I don't really see that often
Most people dropped Dante for Vergil
Viper I don't really see like that
In the end most people's teams are dominated with the characters that I listed + Haggar and Sentinel. The game is repetitive and needs balance patches, but shit is never getting patched so it'll forever be like this.
just look at this year's top 8