So they are not really World Champions, so what?

Is there a team outside the US that could beat any NFL team? I think we can say no with confidence.
Is there a team outside the US that could beat any NBA team? Debatable but the NBA is by far the strongest/deepest league in the world.

There are other many other sports which have minuscule participation in a global sense. They have genuine world champions in the sense that anyone is free to compete/enter but in reality there is very narrow interest. Is being the World Champion in floorball more noteworthy that the NFL champions?