I felt bad winning the Charizard/Bowser Jr. match because I got outplayed up till that very moment. I had no idea what to do about Rock Smash.
I must be the craziest Peach in the world because I can't do this. I don't possess the patience and Mac just barreling down on me makes me nervous. Plus, like you said, there isn't much Peach can do either.
It isn't really a good tactic. It's just boring the other player into making a move. It wouldn't work in a real competitive setting, because opponents would be willing to wait it out there, so there's no real reason to ever do it aside from trying to get your win/loss ratio up in a really dull and boring way. If I find a Peach doing this consistently online, I just disconnect. I don't want to waste my time like that.
I do kind of wonder if Mac has a good tactic for beating it, but again, it's kinda pointless. Since neither player can really do much during it, it's just a time waster that advantages Peach if Mac gets impatient.