strong characters are not invincible. people use this exact same logic to downplay big mom and its kinda stupid tbh.
Mudman is really overpowered, it was mainly his quirk that was trapping machia. And I don't see what is so wrong about that. His quirk literally allows him to turn things into quicksand.
Not to mention they were also using other quirks, like minetas, which specialize in trapping opponents.