Plenty of countries have national parks btw. Many of them had them before America.

Well not really though ? Yellowstone established in 1872 is generally considered the first national park, in the modern sense of the term*, and inspired others to follow in the next couple of decades in Canada, New Zealand and Australia. It wasn’t until the 1900s that the first national park was established in Europe.

• there are a couple of other places that also claim this distinction, depending on how exactly you define what a national park is, but not many

Calling national parks “America’s best idea” is a quote from historian and environmentalist Wallace Stegner - I think the point of it is not to toot some US exceptionalism horn - in context it’s more of an acknowledgment that America deserves a lot of criticism - saying that national parks are America’s best idea is actually putting a bit of shade on other American exceptionalism claims, especially during the Reagan “shining city upon a hill” era.