I would imagine putting on the pounds would make his long term outlook as far as leg and hip pain are concerned worse.He looks a little thin. They should feed him more, though I can imagine his food bill is already extraordinary.
As you well know there can be huge variation in a breed, but I agree this "Dane" has something else going on...He doesn't look like a purebred. I am no expert in Great Danes but I know windhund dogs (windhund, sighthound, racing dogs, etc), and he looks like a mix.
Look at his lower back, see that it goes down in 45 degrees? That's how it is on the windhunds. Those visible ribs are also one of the characteristics. I am assuming that he inherited whose long tall legs from the windhunds too. Take a look at these pictures and see what I mean. You know that some of these windhunds are very tall dogs. Not all of them tiny like the grayhound, but the "built" is the same.
Maybe that's what made him so tall?? It took his natural height and added that tall long legs proportion and you got that tall Dane. :dunno:
Grayhound (can be up to 30" shoulders high)
And of course the real grayhound
Or maybe he is just deformed.