Damn right I got my understanding of Rugby spot on... I play it
I'd hesitate to say that either NFL or rugby players are "better" athletes than the other. In the top leagues, both sports have the finest athletes around, within their respective sports.
I've never played football, but it seems rough enough to me... The fact that you
have to wear helmets and pads says something towards that. But rugby can be pretty dirty... There have been people who have had their ears bitten almost off in the scrum... Something the helmets prevent.
I'd say that the greater speed and force of collisions is merely to do with the way the game is played. In rugby, noone is looking to get tackled, and will be twisting away to try and break through the lines, meaning that the tackler hsa to be on his toes, and can't simply smash into him full pelt.