Sentinel allows for the excessive meter building and damage after the initial DHC because drones are immune to hitstun decay. Frank does not have an assist like this. I would also personally rather have drones for Magneto instead of shopping cart. So I'm not really feeling Frank on this team. Dr.Doom on the other hand... swap him out for Sentinel, and he fits like a glove.
I never play online, I find the lag makes it unplayable. I honestly don't think I'm a very good marvel player anyway.. I actually rarely ever play against people, I just putter around in the lab trying to do science. ^_^