Cloud's hair looks flattened because I'm not good at making it stand up and look halfway credible :x;;
And, well... when Michi-sensei finally settled on a design for Hamel, he had such skinny arms it really gave the impression he wasn't that well-fed. Add his wasp waist, his eat-and-run tactics and the few times he was drawn shirtless in the manga, and you reach the fanonic conclusion that he's a lanky twig.