At least Yamcha recognises his limits and retired to do something productive rather than just hanging around needing to saved all the time. Hell, he even has a unique skill that he's so good at he managed to beat a team of the strongest warriors with in it the baseball episode. He also stepped back up to the plate for the Galactic Prisoner Saga and managed to not get, well, Yamcha'd in it.
Anything Aquaman does there's someone else on the League that can do it better.
(I like Yamcha, alright, don't @me)