If they're happy in their own small pond, then so be it. As long as they understand the boundaries of what they've accomplished, then I see no harm in letting them enjoy their moments in the spotlight of the small stage.
Calling someone "the best in the world, bar none" after such a competition is akin to winning the championship in an independent football league. Maybe they did do some truly great things, and maybe some of the players could make an NFL roster, but it's not the NFL...
If they want to test the larger bodies of water, though, all of the flash and show isn't going to be worth much at all at the national level (USA-NKF), much less the world level (WKF), and that's assuming that they'd even qualify for the US team.
They'd better be aiming a bit higher, if they want to be mentioned in the same category as names such as Kotaka, Au-Fonseca, etc.
Then again, if they don't want to do such things, then so be it.