So what? It's "horses for courses" a marathon runner is never going to win an Olympic gold for weightlifting, and a weight lifter isn't going to win an Olympic marathon. Neither is better or worse than the other, they are just tuned to a specific sport. Likewise with Soccer an American Football, both are atheletes but are conditioned for different environments.
As for the "World Championship" claim, it is just symptomatic of trying to hype a very small tournament into something that it isn't. What does it take to win the Super Bowl? Not much - 16 teams play a four round playoff series to determine a winner. That's not much of a tournament. Compare it to the English FA Cup (in its 137th year) which is a separate, but parallel, competition from League matches.
731 teams entered the competition last year, there are two preliminary rounds, then four qualifying rounds, then six Main Rounds followed by a semi final round and a final.
The smaller teams start at the preliminary rounds and the semi professional teams get added in at various stages until the top two professional divisions join at the third round proper. There is no seeding and it throws up some fascinating David v Goliath matches. Winning the FA Cup is an achievement to be proud of, but it is only regarded as a National Trophy.
Fine.
When Spain, Australia and Zambia get American football teams and they want to compete against US American football teams, then will you be happy?
Until then, the NFL Champions will continue to be WORLD champions without having to compete with other nations BECAUSE the other teams DO NOT EXSIST.
If there was only ONE TEAM in the world that played 43-Man Squamish, then they would be WORLD CHAMPIONS AT 43-MAN SQUAMISH!
http://en.wikipedia.org/wiki/43-Man_Squamish
I would suggest your next step is to sue the NFL for improperly using (according to your lexicon) the meaning of the words “World Champions”.
Have a nice night.