Problem with the old move set is, it's terrible. Am not against the idea in general of bringing back old move sets / playstyles through new characters. For example, Melee Peach was way more campy and defensive. Daisy could be made more like that. Or N64 Pikachu being a more powerful overall character, use Raichu for that, give it the old aerials for example. Or what about Pit and Dark Pit? Just make Pit more like his Brawl self and keep Dark Pit more or less the same. Just saying thing, not necessarily "for" these ideas or anything (I think Dark Pit and Daisy as Echoes are fine enough and don't warrant more for example).
I just don't think Bowser in Melee and Brawl had a good enough functional move set to bring back. And Dry Bowser is a perfect alternative costume. He's still Bowser after all and works with the same animations.
And I mean he's just functionally bad, as in, he's bad at being a heavy weight due to how his moves link together. Bowser in Melee and Brawl really can't do much at all. He's just functionally bad, the character has serious flaws that will always make him a weak character overall. Same with the current designs of say, Zelda, Little Mac, Lucario and Ganondorf.