It is an interest idea and a great starter for philosophical thinking, but no-one is treating it like literal gospel.
Of course not. "Gospel" is a religious concept. They're claiming that it's a plausible, scientifically-supportable theory.
I don't think it's an interesting idea at all, nor do I think it's a good starter for philosophical thinking. I think it's Creationist nonsense.
In what way would you propose to test the simulation hypothesis by experiment?
(* I'm assuming you're using the word "theory" loosely here.)