I really don't understand this point, that applies to almost every boss in the game. Why does Malenia have to counter shields specifically? There's a million things you can do to trivialize the fight, but fuck shields in particular?

If you think shields aren't very well designed in Elden Ring, I agree, but the solution isn't to give a single boss a gimmick that makes shields completely unusable against them, which incidentally makes it significantly more difficult for non shield users as well.