It's not a matter of what my ideal of masculinity is ( in my view it's an outmoded concept ). However I don't think the below would work quite as well if Dom was built like a tank, with bulging thighs and calves. And obviously building muscle is how you compensate for specific areas of weakness after injury.
And by the way, I like this picture a lot; to the extent that it is provocative it's good art, Dom just looks cool in it and it breaks down barriers. However, I just wonder whether his leanness is beneficial to his injury recovery.