Rugby was my first sport and since coming to the mainland, at 10 years old, switched to American style football. Also playing some rugby weekend games here, since a teenager. First impression of American style football... easier compared to Rugby. Also played a bit of Australian rules football, which for the most part, makes American football even easier. OZ football, for wild men only.
Can't knock American football, played 4 years at Division 1-A and playing weight at between 265 to 285 senior year. But as far as stamina (endurance & strength) go, Rugby and Oz rules football is way ahead of American ball. Can say any is better than the other, but there is a difference between rugby and American ball. I had three relatives who played in the NFL for a number of years.
I've seen rugby players from Fiji, Samoa (both groups) and Hawaii who could do well in American ball....no doubt. The percentage of Samoan & Hawaiian players in the NFL is very high, considering the small population of that racial group. We are just stronger, an accident of birth and genetics.
49'ers didn't give full advantage to that rugby player, very obvious. Some teams better pick him up, to their advantage. GIve him a year...and watch out. NFL clubs keep making major mistakes year after year, as far as players are concerned.
Far as Culter goes, he would not last the first week of rookie camp. Being strong is only the smaller part of being a NFL player. Timing, quickness & speed (not the same thing) are prime qualities looked for in a player. Perhaps the number one quality is heart, the shear will to win at all cost. If your only ability is to stand in front of a mirror, for hours, and flex..than maybe NFL football is really not for you. Maybe even high school football is not for you either. Some local kids play near 300lbs and as quick as lighting, 400lbs plus benches...etc..