'Better' is relative. I see Olympic sprinters, etc., go on to the NFL. RG3 just missed the Olympics as a hurdler and he's a quarterback. I'm not sure about world class athletes playing rugby. Maybe there are but I haven't seen them.
I'll bet there isn't a guy playing rugby that wouldn't jump at a shot at an NFL contract and there's not a soul in the NFL with any interest in rugby. I also have never heard of a rugby player that was able to obtain one of those NFL contracts.
Different strokes for different folks.
