I'm going to have to disagree. For a game like this, I think online will be filled by characters who fall into one of two classes: Popular characters and zoning characters.
The reason being, the vast majority of people getting this game won't tournament players looking characters with good tools and such. The casual players will pick their favorite characters--the popular ones--and hop online with those. The others looking to win and win easily, will gravitate towards zoners that take advantage of players inexperience and lack of mobility. Just like MK9 was filled with online Scorpions due to his popularity, and there were tons of Ermac players abusing his lifts into easy damage. If I had to guess, I'd say there's going to be a ton of Batman/Joker players to due to popularity/story and lots of Green Arrow players taking abusing the newer players.