I don’t think the MCU has had an epically bad movie like SW but they have had bad movies. Thor 2 and Iron Man 2 & 3 are pretty bad. But they all did pretty well.
Also consider when Lucas was in control he withheld a lot of stuff from toys, games, and films for years and when he allowed them back fans ate them up. Now you can find just about anything you want.
Point is the belly aching for SW didn’t start until after the 90’s and has increased because “purists” haven’t got their way and it’s not as special as it once was. Compare an Avengers movie event to A regular SW event and we see something totally different.
I don't know what you even mean by the difference between an Avengers event and a Star Wars event.
Bellyaching about the creative direction of a movie franchise is done because of investment in the franchise. I don't know whether
you count that as loyalty or disloyalty. I don't know too many people who are "done with Star Wars," but I do know some who say they hate certain movies, which I would say indicates they still care about the franchise as a whole, and if that criticism counts as disloyalty, would be right back on board with another good movie.
It's when they stop seeing the movies and are indifferent to them that you find out how disloyal a fan base is, sort of like what DC is doing.
I'd say that the masses aren't loyal in general, they just want to be entertained. The hardcore fans can go either way. There are comic book fans who hate what they are doing with the X-Men movies, but those movies are still wildly popular, and creating a new fan base alongside the comic fans.