There to me is a big difference between an amazing game that does a lot right, and being game-changing. Game changing for me means it changed the industry after it, but WoW was kinda the last of the big MMOs that were successful. Everything that came after it – with the possible exception of LoTRO – kinda failed on liftoff: Matrix Online, COH, Vanguard).
WoW by definition changed the industry, so much so that no other MMO that came after could succeed. The iPhone did nothing new, that is regarded as a game changer. Tesla is regarded as a game changer, despite the fact the lowly Nissan Leaf has sold significantly more electric cars than every Tesla model combined.
Game-changing refers to changes in the marketplace/industry as a result of a new product. WoW is the definition of this in games.