Of course any sport or activity would get much more competitive if every athletic young person devoted themselves to it. So your point is very valid. But I would disagree that to say because Megatron is large, strong and can catch extremely well that he would be on top of the DG heap if he wanted to be. Would he also be the best placekicker, QB, or RB?
Consider that a giant sample size of young athletes play Baseball, Football, Soccer, Golf, and Basketball. And yet very few of them make their Varsity team. Even fewer make it to College, even fewer a starter at a D1 School, even fewer to the professional level. And even after all of that whittling down, there are standout all-stars in the pros.
So who would be the stand out all stars in DG? Megatron may be my top pick for WR, but would he be for DG? Probably not.
Sidenote: Don't discount the athleticism of guys like McBeth, Lizotte and Wysocki. Not every great MLB pitcher is randy johnson sized.