I don't agree about the compression issues at all. As you point out, it's established in the AR that speeds are greater and that transporter and (as of this film) comm systems can cross distances that they couldn't in the old continuity. I think the films are very consistent on this point and it is not at all a mere case of "it's time to set our next set piece in front of this scenery." It simply makes the part of the alpha quadrant where Federation and Klingon space are smaller and (I suspect) makes it easier for the writers to dream up entirely new locations and situations for the five year mission.

As for Marcus, I quite like what the did with the character - after all the crazy shit that went down in the 20-some years since the Kelvin incident, of course there would still be a Carol Marcus and she would still be a genius, she'd just go into a slightly different field.