I'm not so sure that Activision/Blizzard overcoming their current woes by releasing a better updated game is going to be problem for Square Enix. I suspect it will drive other competitors to up their game and bring about another round of gaming companies considering releasing some form of MMORPG, since the top two such companies appear to be doing well.

As always there will be winners and losers. The "losers" still bring in a hefty amount of money, or you wouldn't see older MMORPGs still churning out content releases. Even Ultima Online is still up-and-running as a subscription-based MMORPG. Some games retire after a few years, some continue on for decades. There is no right or wrong game to play, nor is the gaming community stuck in a zero-sum competition for players.

At least that's what I see, based on about 40 years of playing multiplayer RPGs. (Circa 1983: Scepter of Goth: a text-based multiplayer RPG with 16 maximum concurrent players with a subscription to play).