But even then in the best-case scenario that's basically giving up having another character so you have to be really sure there's not some other more interesting character you'd want instead!

The W-Engines in ZZZ feel very... ancilliary. I think that's the term. Sure, they do offer a bit of stat boost, and a passive, but unless you're trying to S-rank the hardest combat missions, you don't really need the character-specific ones, or to max level them.