Pac Man actually does pretty well against the top tiers because he's got so much **** to handle their approaches and control the battlefield. Specially with customs. The weird spazzy fruits, fire hydrant and meteor trampoline are pretty fearsome while not being janky like most customs are.
I won't say he's even against them, but he can definitely surprise people because he's such a deep character. I'll say that once you start learning his tricks it becomes a tad easier to look out for specific stuff, but he can still hold his ground pretty well. I'd say one of his worse MUs is Rosalina, but there are plenty of characters that can deal with her. Plus, Rosalina is not so top if you know how to fight her.