Mickey is Walt's most famous creation, and to this day is a far more timeless and popular IP than anything else. And so I believe that a Mickey ride does indeed have business being at the center of the park. Shouldn't have to replace GMR, it should be built in addition to it. But he is the heart of the company, and so I wouldn't pull out my pitchforks and knives if his ride lands at the heart of the park.
Guardians of the Galaxy is the latest movie flick. I liked the movie. But it has no place in the company's history or in the history of movies. Would make a wonderful ride, but as Martin said, not in the center of the park. It has no umbrella aspect to it, and it is almost as far from the heart of the company or the heart of the movie industry as one could get.
Even from the standpoint of a dumb exec, a Mickey ride should clearly be the better option. Mickey is more popular, more timeless, and more of a merchandise seller that GotG ever was or ever will be. I suppose that's where the "dumb" part comes in, they don't realize even the most obvious things.
In the end, I root for The GMR to stay. But if something had to replace it... I'd hope they stick with the smarter choice.