It's not silly at all. If you took the top 20 skill position players in the NFL and had them go back to 5 years old and told them to play soccer for the next 20 years instead of football you don't think they could develop the ability to play the game at an elite level? Come on. The skills sets in football and soccer are very similar (unlike golf to basketball or baseball, or soccer/basketball where height is a critical factor as you suggested). Strength, speed, quickness, vision, jumping ability, exceptional feet, etc. Of course, they would need to learn how to kick the ball but it's no different than learning to catch a football. They became elite football players because they practiced day after day just like the guys now playing in the EPL, etc. did with a soccer ball.