Marvel has more or less done the same. None of the comic book movies, regardless of the franchise, have been truly faithful to its comic book origins. And even the comic books themselves change the story lines every once in a while.
Steppenwolf as the main villain of "Suicide Squad"? God, what a dumb idea. It's a good thing David Ayer changed it. It just would not have worked, as far as I'm concerned. It would have ruined the theme of the movie's plot. And the Enchantress made a better contrast to Amanda Waller than Steppenwolf would have.
I agree that the Squad should not have fought him as the main villain but It would have been nice to see Steppenwolf manipulating things toward a goal.