I assume you mean FD and SV... I don't think SV is particularly unbalanced in most matchups, but FD is definitely a counterpick and a horrible starter. If you want to see why, chew on this figure for a moment: it was banned in 1/3rd of all the total sets in MLG. You know, the tournament series that also had Norfair, Green Greens, and Pictochat legal? The stage is wildly unbalanced, and heavily favors certain types of characters, despite its flat, unmoving ground.
SV gets dragged into the discussion mostly because it favors exactly the same characters as FD, although not quite as extremely. So when it comes up in the context of starter lists, I just feel obligated to point this out:
Diddy's best 4 stages: FD, SV, Picto, BF
IC's best 3 stages: FD, SV, BF
Falco's best 4 stages: Japes, FD, BF, SV
This is what I'm talking about when I mention that the stages are unbalanced. It's not a problem iwth 7 or 9 starters, and it's not a problem in 5 starters if FD is gone. But the typical 5-starter? Yeah....