Most do and i'm completly fine with making such an assumption on behalf of nearly every watcer (there is always an exception somewhere) But where it starts to fall apart is how much of it is an act it varies from vtuber to vtuber which is where simps slip through the rather large cracks.You'd think that by now people would realize that it's a bit convenient that most female vtubers happen to do the whole "I'm cute and dorky but also super shy irl uwu" thing.
It's pretty much always an act to some degree. It's fine to enjoy the act. Anyone who falls for it to the point of getting angry when the act is revealed (in their eyes, at least) should have known better, though.
Especially for the Terminally online who don't know the difference between Friend and online "friend" hell even not stupid people can find reality and an act hard to tell the difference when they do not have much reality to go off of.
How Stupid is Gura exactly if it's an act shes really damn good at being convincing. Just as one example that i think even the most waterlogged fans will have trouble giving a concrete answer.