Oh and also it was betrayed by its own trailers, I think. Kang wanting Scott to help get something is like the main point of them, but that's like late second-act, third-act stuff. So much of the movie is about getting to that point. The tone of the trailers should have been more "oh shit we're trapped in the quantum realm and it's being run by this oppressive bastard" and then it's revealed to be Kang in the final seconds of the trailer.
I know, "trailers give the movie away, more at 11," but they should be savvier about this stuff now imo. This is even more egregious than Ragnarok being all "the Grandmaster's Champion is terrifying Thor might be killed by him" for 15-20m when everybody knew already it was Hulk