It's a lot harder for Marth to win based on attrition in a game with stages like Rumble Falls.Not to mention Marth does not need to rely on gimping since he can win based on attrition alone against the characters he can prevent from landing.
As far as percentile goes, Marth is just as good as he was in melee in PM. Maybe minutely worse. There are a few characters, not more than a handful, (Fox, Falco, Sonic, maybe Pitt) that are better by design and then there are a few that just give him a stupidly hard time and have to play less perfect than he does to beat him (Sheik and to a much lesser extent Puff maybe 1 more) and then there is everyone else that Marth either beats or does fine against.
I also think that a lot of characters in PM are well-equipped to deal with dash dancing, at least compared to Melee.