7 characters in top 8, 8 if you count Iluusions as deadshot or arrow. He won key matches with those 2 including Black Adam. Even if you count him as just Adam, that's 7 characters. Scarecrow, Batman, Adam, Aquaman, Atrocitus, Darkseid, Superman.
Catwoman had a lot of success, as did Harley, but neither character quite made top 8.
I really don't see the issue with character diversity, considering this is the release version of an NRS game. Robin and Bane were deep in the bracket(who were both in top 8 at CB), a few Cheetah's made top 48. King Raj was in top 48 who is a Firestorm, Steve closed out a win over Tekken Master with Grodd, Green Lantern wasn't in top 16 but had multiple representatives well past pools.
Boohoo Black Adam and Aquaman will show up multiple times in top 8. This is better than MKX before October 4th without a doubt and it'll only get better.