all studios make changes.only Fox gets hit over the coils for it.
I've said it before and I'll say it again. The X-men are/were?

popular. That popularity is a double edged sword.
They were a known brand before the movies meaning people were salivating at the thought of an X-men movie.
But they were a known brand in that everyone knows their storylines based on the comics and the cartoons. So when an adaptation deviates from that people call foul.
So when they put Fly-girl Angel as an original student before the likes of Cyclops and Jean, people don't like that. When Halle Berry talks without an accent, people take notice. When Mystique is shoehorned in as Xavier's sister, people complain on message boards
On the other hand, Avengers were barely popular before the movies. Sure they predate the X-men and sure people know Cap, Ol' Shellhead, Hulk, and The God of Thunder but even their cartoons weren't that popular.
So Marvel can change a few things up from the comics and as long as the end result is good, as the movies have been, then everything is hunky dory.
So when they put Hawkeye as an original member before the likes of Ant-Man, people couldn't care less. When Scarlett Johannson talks without an accent, most people wouldn't give a Mickey's arse.
(I'm trying to think of the equivalent of changing someone's sibling in MCU after it's been established in that same film continuity to not exist).
Also doesn't help that I'm a bigger X-men fan than an Avengers fan so I know all the spoilers and the plot before a movie comes out and so it kinda ruins the movie-going experience and so I'm more highly critical of the X-verse. But I wouldn't have it any other way. Following the productions is half the fun.
sometimes it is difficult to respond to valid arguments, isn't it?
You tell me.