I agree with your last sentence, but I am of the opinion that one should see much of the US sights before going abroad to see natural beauty.
The world as a whole offers more than the US, but the Grand Canyon, the Tetons, ea Canyon, the Painted Desert . . . These are unique places and “real sights,” and well worth seeing before taking your sightseeing money to foreign lands.
OTOH, if your big thing is antiquities/history, then the rest of the world has a lot more to offer. Ditto for many types of wildlife.