I think that's all true and fair, but I think it's largely due to the source material. You can only make a DB character so different from his or her peers.
Piccolo could do a lot more with stretchy arms. Beerus' balls could be more dynamic and useful. Buu could do a hell of a lot more with his stretchy gummy nature. I think Gotenks should do more crazy shit, since his whole thing is coming up with nonsense like kamikaze ghosts, but unfortunately he's basically gone to the wayside in the actual show, so they've had no opportunity to provide more move types. Hit's cool? Nappa with a bigger focus on the saibaman gimmick could be really cool, but I don't think it'd fit his character to do too much of that, sadly.
I think that's all I got lol
Ginyu already has a large focus on assists, which I think works well for him. I'm a fan of Yamcha's nonsense, even if I'm garbage at it (and I have no idea if it's even any good).
It's true that a lot of characters in Dragon Ball have extremely similar attacks, but there are some that stick out, and I feel like they're woefully lacking in taking advantage of that.
Also tbh Adult Gohan should be much more of a bruiser. In the show he's basically just fuckin' brute force (despite ostensibly being The Smart One). But that's not so much a solution to this problem. Just a nitpick I've had since the beginning.
