The problem is that, with such a great cast, your acting mistakes are highlighted even if objectively you're not that bad. Take the character of Dylan (Max Thieriot), he's not bad or anything but you can clearly see how subpar his acting is compared to the rest of the crew.
Gaga's acting wasn't great. She's very theatrical as a person so she managed to pull of some scenes, but most of it wasn't that good.
Not to mention that the whole AHS cast and their acting has decreased in quality significantly. It's not their fault tho, you can't slay a bad role no matter how great of an actor you are.