I'm curious what you mean by him not having the body type for today's tennis - in my head, he's 6'4ish, appears to be a predominantly fast-twitch type of guy (which most people are born with a certain proportion of fast/slow twitch), can serve 140+ with little knee bend or torso rotation, and has decent wheels - based on how rounded his upper back/neck is, it looks like he suffers from the typical "text neck" and isn't doing enough weight lifting to overcome that poor posture, which is probably leading to his neck issues. Based on his overall physical appearance, it doesn't seem like he invests much time in the gym - I don't see why, with a tiny bit of effort, he could at least look physically get to a zverev-esque level (by no means "muscular", but strong enough to fix muscle imbalances, prevent injury, and maximize his potential).