I do see many online reviews of gravel bikes where they are testing them on what I would have considered mountain bike trails in the 1990s. I don't really consider single track through the woods "gravel riding". In fact, that was prime 26" MTB territory in the 1990s. But every reviewer seems to test their gravel bikes under these conditions.
"Gravel bikes" were more or less developed for riding gravel roads, were they not?