Why would you put the most extreme situation on either side of the example? I never said you could turn pro after downloading the game in 3 weeks. That's ridiculous. We're saying the barrier of entry is a lot lower. Assuming you're good enough to turn pro in LOL, all you really need to do is download the game, get into challenger and you can probably make a case to get picked up by a team at that point.
Football requires a lot more time, dedication, training, money for the average pro NFL player. There are always exceptions, but the average player is playing the game for at least 7 eyars.