There's the whole Ginyu Special Squad, we don't really need more second-rate characters. Sure, Zarbon has a transformation, but that's about all. Ginyu Special Squad is wrapped in a buddy system.
Tenshinhan won't be in because it was up for the community to model and animate him, and the community failed. Though I imagine his Kikoho would be the most dangerous technique in the game, thanks to it being much greater than Kamehameha and also spammable.
Cell is in.