But what if World of Warcraft had been released onto a market where the already existing competitors were not so much different in quality? Sounds like a stupid hypothetical question, but I feel that something like that is happening now: Blizzard is soon to release Heroes of the Storm on June 2. It is a nice, accessible, polished game like pretty much all Blizzard games are. But it isn't much better or much more accessible than the competition. Yes, there is a training mode against the AI to test out new heroes, and some rules changes are designed to limit asshattery between teammates during a game. But it competes with a League of Legends with 27 million daily players, not an Everquest with 400,000 subscribers.
I am pretty sure that Heroes of the Storm will get millions of players, and that some people for different reasons will prefer the Blizzard version over the Riot version. But I don't see Heroes of the Storm being a "LoL killer". It will be somewhere in the list of the top 5 MOBA games, but not necessarily number 1. Blizzard is really late to this market (which is somewhat ironical, seeing how they could be said to be involved in starting the genre), and the existing games are already highly polished and accessible for a multi-million player mass market. The WoW/Hearthstone effect of "I'm taking a niche genre and make it accessible for the mass market" just isn't going to happen here. And thus I doubt that Blizzard will have such a huge impact on the future of this genre than it had on MMORPGs.