I think your construct of "extroverted athletic confidence" could describe people like Ray Lewis, Dan Marino, and Jerome Bettis, and not touch at all the problematic aspects of BPD (impulsivity, unpredictability, emotional lability, interpersonal difficulties) characteristic of people like Marshall, Terrell Owens, and Chad Ochocinco.i.e. what he shares with the media and how the media contextualizes it. Referring to the information the media has covered of him at this point and what we are judging his personality by.
I don't think Andrew Luck would have any problem getting along with the "confident athletic extroverts" of the world, such as Lewis, Marino, and Bettis, but the presence of people like Marshall, TO, and Ochocinco -- precisely because of their larger personality problems -- would impede his development IMO.
Again, the problem with people like Marshall is they do not possess the ability to rein themselves in when the circumstances dictate. When you have a young QB who needs to develop as a player and the leader of your team, you need to shut off your "get me the damned ball!" attitude during that period.
People like Marshall, TO, and Ochocinco don't have that ability because their personality flaws are exhibited too rigidly, without consideration for the situation.
Marshall would still be able to be "confidently extroverted" in an athletic manner (like Lewis, Marino, and Bettis) with Luck at the helm, but he would need to shut off his selfish, infantile, demanding traits, and he can't do that. Those are woven too deeply into the fabric of his being.
Those traits are on "auto-pilot" -- they don't "care" whether Andrew Luck is around or not, and that's the problem.