while Amish are most certainly human their existence rests on the fact that they happen to be surrounded by the mean old United States. Any moderate historical predator would otherwise make short work of them, they're a fundamentally uncompetitive civilization.

This goes for all utopian model communities, Kibbutzim, etc, they exist by virtue of their host society's protection. And as such the OP is right that they have no impact on the course of history, because they have no autonomy.