Dragon Ball Z was a victim of it's own sucsess, the mangaka actually wanted it to stop after the freeza saga (which actually seems reasonable), but at the time it was far too popular and he was forced to continue which is what caused a lot of the problems people have with DBZ. DBZ's popularity was still affecting it at the end of the Manga, the mangaka actually wanted Gohan to be the final hero of the series (DB was Goku finding himself, DBZ - Freeza Was Goku Becoming a man and avenging his race, the rest of DBZ was supposed to be Gohan becoming a man) but the insane fandom of Goku forced him too change the ending (which is why Super Buu turns into the weaker Kid Buu and SSJ3 Goku defeates him). The series was further damaged by the Anime-only series DBGT which the mangaka didn't even want and was not a part of. There are similarities between the big three now and DB/Z because the Mangaka now grew-up watching/reading it. One Piece is one of the most original shonen manga we've had in a while and it does have some similarities with DB/Z (Just like future manga will have similarities with One Piece), but saying is only just begining to become like the DB series is shallow, OP has always had similarities to DB but was never anything close to a mere immatation; OP is thing of it's own.