I don't think climbers are anything much harder to learn versus, say, fox, lol. Their grab combos, while maybe difficult to do at first, seems fairly doable once you get it, especially versus fast fallers.
If Falcon can win tournaments, I think Jiggly can as well, though, the deciding issue is how they handle Marths. Falcon has the speed, Jiggly, not so much, lol.
Oh yeah, there's also Peach, she could win some tournaments as well, but she seems to have fallen off in popularity a lot.
Edit: Though, about Climbers, come to think of it, their big strength is when they're together, and it's fairly easy to **** combo Nana, though maybe could Climbers can figure out a way to disrupt that, I dunno.