Agree. He worked out a lot last year and probably is the strongest among players in his age (comparing to Dimitrov, Tomic, Stebe, or a little older Raonic, Nishikori). Look at his neck....
He has a lot to be improved but his body strength is not the priority.
Yeah, he's strong for 20, but not strong compared to most other players, has to improve stamina/cardio, not just muscles.