Her punishes are more consistent and don't require sweet spots; say in Marth vs Peach if he doesn't kill her with a tipper or a spike he has to get her up to like 180 without a setup like dancing blade > utilt. She's better at dealing with campers and does better than Marth at some of his harder matchups (Sheik, Falco, Climbers). I feel as that the metagame has shifted towards more of a "camp until you can get a hit" that Marth has a harder and harder time as he can't just throw out moves or he'll get baited and punished. She's been outplacing and outperforming him for a while now. We haven't had a Marth player be dominant in ages, and usually he is only used for specific matchups or stages instead of a stand alone character. I think there's more to it than Peach players are better than Marth players; there's a reason he can't compete in this environment and his growth has really staled the past couple of years. Until PP had some success at Apex I felt like Marth was going extinct for a while.