Doc had plenty of ego as did Rondo, Ray, Pierce and KG. That the Big three were able to submerge their egos and work to a common goal resulted in by far the biggest turn-around in NBA history with a very young PG. They won the crown in their first year, which is pretty amazing in itself and started the following season with the greatest start in NBA history until their MVP went down.
I don't think the locker room was bad at all. It was a strong locker room with a strong coach and a strong GM too. If Rondo, the Big 3, Doc and Danny had small egos, they wouldn't have amounted to much.