Speed, during the middle of most battles, isn't really useful enough to justify Dance as a good move. You rarely get what you want, and it only affects one at a time so you could just use Lucas, Kumatora and Duster for Offense and Defense.
Also, while Boney may be fragile, Salsa isn't any better at taking hits either, they have about the same max HP and Defense stats, but you'd actually want Salsa to take hits for Monkey Mimic and someone has to heal him after as well.
Boney is probably the most reliable damage output in a boss fight. He's going to be either bashing or using items, most of which would be bombs or rockets. Most of the other characters will spend some turns on support moves. His Speed stat also means he's better at using certain items since he's practically guaranteed to go first.
In every boss fight I have to let him die because I rather prioritize Lucas / Kumatora and some of Duster. I didn't like wasting time on Boney because I just felt he didn't contribute enough.
That's odd, I never had that problem.
For me, yes, he needed a heal sometimes but he rarely fainted.
We probably have different playstyles.