Uhh... I'm more concerned about Murray missing a season because of development, but I'm not concerned about all this "game shape" stuff you are talking about beyond the concern of every young kid.
I don't know how much he can push that shoulder, but I'm pretty sure cardio and lower body aren't much of an issue.
I have less concerns about Murray than I do about Prout. He played very well last year and there is probably no reason to think he shouldn't do just as well this year. But it just seems there is that sophomore thing that seems to jump up and bite so many.