The problem with your thinking is that promotions at that level are based on COMPETENCE not heroics. His stint at hanoi hilton was absolutely irrelevant as far as his ability to command SHIPS(and thousands of men) properly. If you look at his career objectively you will realize he had no chance in hell of matching his father's and grandfather's achievement. There is no shame in retiring as captain unless you had family that achieved much more not once but twice. This is not a minor thing people last name McCain used to stand for a lot in the US Navy and I have no doubt he even got captain because of it.
I have learned officer ranks of the US armed forces some time ago, nobody is going to lecture me on it. And yes I was fully aware of the fact that the Captain in the US navy is in terms of pay grade equivalent to Colonel in other services. The difference between Captain and Rear Admiral Lower Half is so much that there is a tradition in the US navy that when an officer reaches flag officer rank (begins with Rear Admiral lower half)all the other flag officers write that person a letter of congratulations.
What about his injuries/political aspirations, didn`t they play a part? Senator Mccain retired at the age of 45, his father was promoted to rear admiral at 47 and his grandfather at 57?
Do you honestly believe that it matters a lot to an admiral whether he can fully raise his hands? If you look at McCain's biography you see several crashes and his stint at Hanoi Hilton. Do you want to groom senior US military commanders based on their being captured? I would not do that. You look at competence and successful operations. Being shot down and captured is NOT a success.
Do rear admirals only sit behind desks? How would a competent pilot avoid being shot down by a missile?
Having a SAM blow off your right wing in combat is not necesarily the perceived failure you'd like to think it is either. Or maybe think being wounded in battle is a "failure". Badly injured and landing in a lake in the center of Hanoi made evasion from capture impossible as well.
To bring up Patton, you serve your country best not by dying for your country but convincing the other guy to die for his country...
To bring up wikipedia here is a passage that is VERY illuminating "...during the early-to-mid 1960s, the planes he was flying crashed twice and once collided with power lines, but he received no major injuries..." Since you try to negate everything I say you will say it was an accident, people have always claimed he was careless. BTW, how could I forget he graduated FIFTH from the bottom from Naval Academy. That is some character! Can't blame North Vietnam for that one.