So I'm not sure that there's a difference between "disrupting" and "competitively innovating". I don't know if it's as easy as your stating, because the F2P market is pretty wide already -- there are a ton of games that you can play for pretty much free in every genre online these days (and there were, when WoW came out, also).

Also, WoW's marketing was the only thing that was innovative about it, the game is subpar in just about every other aspect, IMO.