@OneUniqueFlower yep, she's a mary sue. The ones you mentioned are also mary sues, though, as the authors dont intend on giving them any character flaws, as they are supposed to be "perfect as they are", and everything else around them is/becomes the problem (though remarried empress is arguable). It's basically a trope for these sorts of webtoons...a very, very common one.
I don't mind mary sue's in short doses. They just get boring when say, binge reading. But if no other characters are likable then it gets super boring...