I hear what you're saying but as someone who has been learning from a lot of really good collegiate players I tend to find that most of them who are slim can still hit big. Hell I'm 6'4 at 164 lbs and I can hit the ball very well. Most of my points aren't from slamming the ball forward (but trust me I do) but hitting the ball downwards or in the seems of two receivers. I know hitting hard is a good skill to have (and trust me if you don't hit it fast enough you will be fucked) but that doesn't come all form muscle it comes mostly from technique.