Fair point. And I suppose they could also "Dude" him when he's in He-Man form. It always tickled me that in the old cartoon the only apparent difference between Prince Adam and He-Man was the clothing. If he physically transforms into He-Man, it would make it more believable. It's always going to require a suspension of disbelief that no one seems to notice Clark Kent is built like an NFL linebacker.
There’s this thing you can do to improve your overall physique, build your muscle and muscle mass and get really cut and fit. It’s called working out Haircuts are a thing too I’m told
Posture and an ill fitting suit can hide a lot. Whenever I'm at a weight that's between sizes, my figure looks very different depending on if I'm wearing clothing that's a bit too too loose or a bit too tight.