DD is in no way shape form or fashion as fast or faster than the Flash, the statement made by Booster Gold was purely hyperbole. As for this fight, DD wins, quite easily. No one in Bleach has came across a monster like DD, who adapts to everything, and can't be killed the same way twice.
Why wouldn't Dodoria be able to solo? And Zarbon without his second form was what 24,000? Krillin and Gohan gets stomped here, like I said, Dodoria and Zarbon can each solo, and Zarbon wouldn't need his second form to do it.