I used to play Rugby sevens a while back when I was stationed in Berlin. There used to be a mini-world-cup organised, Consisting of
England
Scotland - There always seemed to be a regiment of Jocks in Berlin
Ireland - Players drawn from the various Irish Bars in Berlin
Wales - There always just enough Welsh types
France
And finally, the good old US of A where invited to attend, they responded by sending a team of absolute monsters. However they always got battered by everyone....They did however beat the Irish once, but the Irish where all completely bladdered from the night before.
Thing is, it doesn't matter how big, how fast, how strong you are - Rugby, and football are team games where skill, running and tactics are the mainstay for eventual success.
I would also like to point out that the Americans were superb after-match company, and they brightened up the tournament with their presence, unlike the French who sulked whenever they got beat!