I don't know if the idea was that bad. Obviously a lot would depend on the execution. I think that once you start making movies where the basic premise is "not reality" (not set in our world, or a period piece, but instead a world with superheroes and/or extraterrestrials and/or magic) you have a very important additional factor to consider: given that it can't possibly be real, how "real" do you try to make it? MCU did it right by making the heroes very human, while clearly possessing skills and abilities well beyond our own. This gives the audience something to identify with. Then you provide plausible explanations for all the "impossible" stuff. We know it's not real, but within the established reality, it works.
I don't see why you couldn't do monster movies the same way. I thought the Brendon Fraser Mummy movies were a lot of fun. At some point, at some level, you believed what was going on on screen despite knowing that it was all "just a movie" with magic and supernatural stuff. I think the old black-and-white monster movies (Dracula, Frankenstein, etc.) could have been updated, made more "realistic" and all that, and had a shared universe. You can make movies outright campy, funny, serious, whatever, and make it work. It all depends on the execution. Set the tone and stick with it, work with it.