Problem is you don't have the data to back this up. Your claim is people started leaving FF11 because they changed it's core game philosophy. What made the Devs change it's core game design? They have access to data that you do not. It's more likely the game was losing players which resulted in a shift on how the game was designed. Many of us have played older mmo's and have quit them in the new age that was introduced to us by WoW.
Of course it's a much smaller share considering how massive WoW is and let me tell you. You clone FF11 with better graphics and possibly updated gameplay and you won't come close to WoW's market share even with it's declining playerbase. I'd bet money you wouldn't come close to the 600k mark either. You misunderstand the point; WoW proved to the world that there is a bigger interest in mmos than people realized. That casuals make up more of the gaming market than the die hard players. Their game catered to the casuals. Leveling become more streamlined, reaching end game became easier, and even after they established their player base they made constant steps to make said game more accessible for it's player base. The end result? The biggest mmo in existence. Many people began to quit their older school mmorpgs to hop on board as well many existing mmo's took massive hits to their player base. So what did they do? They began to incorporate WoW's elements to make their game more like WoW. They aimed to appease their casual fanbase in order to retain subscriptions.
Some mmo's tried to do their own thing while ignoring WoW but came up with a problem. People would drop out of their game and they couldn't get new blood to join. The problem is you act like it was a spontaneous idiotic decision by the devs to change FF11 into what it is now when the decision was probably based off data and research.
*Edit* You also missed my point about SWG. It wasn't about player retention. You asked "Do you think FF14 will be around 9 years later?" My answer was "SWG was practically tearing itself to pieces and limped along for 8 years. FF14 is making an attempt to add in people's suggestions, improve the game, and add in more content while staying true to the original vision. Yes I do believe it will last more than 9 years if it keeps going the rate it's going. An MMO has to practically be trying to destroy itself to lose that much of their core fanbase."
Even if FF14 doesn't maintain the same sub numbers as 11 did in the past it wouldn't prove "11 is better and it's style would have been better than 14." The market is different. The competition is different.