Yeah, this is the point where you can say "okay, it's over." It was such an effortless, easy concept: rip off Konami's Bemani series and use mainstream rock music that the Western audience would actually recognize. It becomes a huge hit with gamers and non-gamers alike. But they had to go and ruin it with corporate greed. If Harmonix and Activision never split up and we didn't get multiple releases each year this could have been a series with legs. It could have been an event type of game, with DLC to fill the void in the year's between.
But it's going to be regarded as a fad because these companies have no restraint and no patience. The biggest videogame franchises are the ones where each game is an event and each game feels essential. That usually means having to wait years between releases. This is like Tony Hawk or Bomberman or Mega Man where the releases are so frequent and break so little ground that they're just there. You buy one game to get your fix and then never keep up with the series again.