I've been watching TFS' playthrough of Dragon Ball Fusions, and it makes me kind of sad how underutilized fusion is in the show. It's such a fun concept with lots of potential. Almost makes me wish there was some sort of alternate timeline spin-off where fusion was more stable and used more frequently.
Interestingly enough, this would also somewhat mitigate the problem of side characters being rendered obsolete by Goku and Vegeta. Characters like Tenshinhan or Piccolo may not be able to rival the main characters in power, but they have a whole pallete of wacky techniques with interesting battle applications. Combining Goku's strength with these characters' versatility would give them some time to shine, and probably also be fun to watch.
Yeah, I know, it's never gonna happen. Goku and Vegeta dislike fusion. I just like to imagine it.