Have you ever played Fox v. Link, dude? It's horrendous.
Falco isn't as bad, but it's still bad enough to be a large disadvantage. Sheik is obviously a large disadvantage because she wins lazily. Fox still has to do stuff that makes it look like he's doing work to win, regardless of how easy it is, which is probably why you're thinking it's not as bad as it actually is.
P.S. - I know very few tournaments that consider the Corneria tactic for Ness a stall; it's not even that hard to get down there and make it back. Ness has no invulnerability down there or any real striking advantage besides going for grabs once you actually get down there. It's not that bad. As long as he's in the lead, I don't see the problem.
Falco isn't as bad, but it's still bad enough to be a large disadvantage. Sheik is obviously a large disadvantage because she wins lazily. Fox still has to do stuff that makes it look like he's doing work to win, regardless of how easy it is, which is probably why you're thinking it's not as bad as it actually is.
P.S. - I know very few tournaments that consider the Corneria tactic for Ness a stall; it's not even that hard to get down there and make it back. Ness has no invulnerability down there or any real striking advantage besides going for grabs once you actually get down there. It's not that bad. As long as he's in the lead, I don't see the problem.