I'll bet there are way more people using the term "power pop" than were using the terms "punk rock" and "garage rock" prior to 1976

I mean, way more people currently using the term power pop now, though whether they're really using it as a genre rather than as an adjective isn't necessarily gauged by the number of people who use the term. For that matter, "punk rock" was used as an adjective as well as a genre term from '71 to '75. (Not that "adjective" and "genre" can't overlap one another.)