I'm sure that was part of it. FFXI was, if I remember correctly, more profitable than expected and for quite a long time was a reliable cash cow for SE. The bosses must have looked at this "success" and thought, "Tanaka knows what he's doing on MMORPGs" and let him handle FFXIV with minimal oversight. I put quotation marks around "success" because FFXI lost a huge chunk of subscribers when WoW came out and never did anything to get them back; they just sit back and let their lunch get eaten by these newcomers. And Tanaka's complacency had a lot to do with that. People would complain about the same things all the time and he would just ignore them. MMORPGs evolved and Tanaka just ignored it. And then it was a new decade and he was trying to release a new MMORPG that didn't learn anything from his years of experience; actually, it was worse than that, he learned that people will put up with anything to pray onrine Final Fantasy geimu and that any and all feedback could be ignored in favor of smelling his own farts.
There were other parts, of course. A big part of it was using an inferior in-house cross-platform engine, "Crystal Tools", which was also a large part of the reason FFXIII was so disappointing. Another large part was that they didn't want to make anything too much like FFXI, so Tanaka ended up being given the very strange and oxymoronic design objective of making a non-Final Fantasy Final Fantasy online game. So we got this weird not-job system where none of the not-jobs were the same as any previous FF game and they just switched everything around for no reason, like giving the stealing abilities to the hand-to-hand class. Also the classic summoned monsters came back but weren't summonable and chocobos were renamed to "horsebirds" (written in kanji not katakana). About that last; another thing harmful to the game's development was the fact that they had to use an incompetent mainland Chinese development house for some of the work, because they had ambitions of releasing FFXIV in China, and the Chinese government requires the use of Chinese companies for at least some of the work (so they can steal their Western or Japanese partner's knowledge and then use it to boost China's economy). Nobody was going to be able to put out a good MMORPG using Crystal Tools even if they were competent, not using Chinese labor, and didn't have to worry about not doing things the same way as FFXI, but I think that Tanaka being Tanaka was what pushed FFXIV from mere "failure" to "almost the RPG equivalent of Heaven's Gate".
