And I'd disagree with gains being optional. It's 2017, dudes like Hemsworth, Jackman, and Evans set the standard for super hero actors. Hell, look how huge Josh Brolin is for Deadpool.
If you want to look at marvel, I feel like you're in a losing argument there. Sure, you have Thor and Cap... But then you have Tony, Hawkeye, Vision, Spiderman, Antman, War Machine, Doctor Strange, etc all being fit but having normal builds. Hell, even Jackson wasn't as built as he is today when he remade Wolverine in his image. He gained that body because he wanted it, but he was Wolverine before he had it.
It seems to me that huge hulking dudes are the highly visible exception rather than the norm.