Bryan Singer did not have unlimited control over X-men. Hell, he came in late in the game. Tim Miller essentially got fired for his vision not matching Reynolds'.
You use the word "creative" control, but that's not what you mean. MCU directors have plenty of room to put their stamp on films with their own creativity. What they don't get to do is decide on the story. And, frankly, neither did the vast majority of the X-men directors. Only Mangold had complete control over any of the movies, otherwise the final product is always a combination of input from the studio, producers, actors, directors, etc.
Gunn doesn't get to make Arrival anymore than Singer got Nightcrawler and Beast in X1. The point you're making has no legs, so please stop dressing it up with the word "creative" in this false and misleading way.