Oh, there’s tons of holes in the magic system, no denying it. It’s used more of a plot device to set up certain scenarios than as a cohesive system (polyjuice potion, liquid luck, unbreakable vows, etc). Which, for a kids/YA series I don’t have a problem with

They literally try this against Harry in book 7 and it doesn’t work because Harry’s cloak is special (it’s one of the deathly hollows)

Harry catches the snitch almost EVERY game. I think the only game he ever played where he didn’t catch it was one where he was attacked by dementors and fell off his broom.

Actually that happened twice, once at the world cup where it made zero sense and once at Hogwarts, where it did make sense, because even though Gryffindor lost catching the snitch kept them in the house cup which is based off point differential