Not really? Her kicks are generally quick and effectively serve as her second line of defense - I've complained about
her Up Smash in particular because it's overtuned. It's
once she's hit that she struggles because she doesn't have a lot of moves to break out of disadvantage (in particular, diagonally below her is a major blindspot). She only has N-Air, air dodge and (situationally) D-Air to do that.
Still though, a competent Min Min player can just wall people out for long stretches of time and tack on loads of damage / edgeguard with ease.
Edit: I'm saying this as someone who hasn't had that much issue playing vs. Min Min either. Also, PSA: Playing against Min Min means that you'll want to mix up approaches consistently and not become predictable. If you can get a damage lead or even a stock lead, great! Also, once one has the advantage, don't be afraid to go full throttle. If you're off stage, mix up recoveries.
Umm...
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Of course,
tier lists are inevitably going to be opinion-based and certain characters are inevitably going to ebb-and-flow (I'd argue that Pikachu and to a lesser extent Aegis are a bit too highly talked about, but that's another topic entirely). Still though, the main takeaway here is that a lot of people have very high opinions of her - and this extends to quite a few Japanese players. Her score averages out really high, which is why she winds up so high here.
OrionStats (which measures results in tournaments from local to international levels and is best as a broader measure beyond the tippy top) shows that Min Min players have gotten a lot of results lately. If anything it reinforces her standing.