I think the popularity of riding on mixed surfaces grew first, then the industry came along with bikes targeted for that usage when they realized there was money to be made. If you separate the technology and designs from the marketing, you'll find some innovation and a whole lot of combining things we've already had. The back story of the 650 A/B/C wheel size tells you the idea of mixed usage bikes is not new at all.
Having gravel and cross and touring and endurance and all-road and commuter and race market segments means we have more choices. I don't necessarily fit any of them, but my chances of finding a bike and/or components to fit my desires is better than ever.