There's actually zero evidence to support the idea that a MMORPG's combat system needs to be faster than a single player combat system. There isn't even any evidence to support the idea that a turn-based system like FF9 wouldn't work with a MMO. In fact there are a few smaller MMORPGs which do have turn-based systems and they work quit well. At the very least those combat systems are more fun than whatever ARR has going on.
Well...FF9 doesn't have a turn-based system... it uses ATB, which is not the same thing. Consider too that in ATB systems in single-player games, you're given as much time as you're given because you're managing 3-5 party members yourself. In an MMO you're managing 1. You would get bored out of your skull if you had to wait 5-10 seconds between all your actions. I realize it doesn't SOUND like a long time, but it is, and it'd add up.
Like I said above I've only ever played 1 MMO that used a turn-based system, that was The Realm Online, back in the mid 90s. While I've never heard of another MMO that did that, it could certainly have happened. If you'd like to recommend one that did it well, I'd be happy to check it out.
You're making the same mistake that Yoshi-P is making in your thinking. "Just because it's not like WoW, it's not fit for an MMO." The global standard is a lie.
It's really not. Please consider that when WoW was brand new, it wasn't even original. It took aspects of existing contemporary games that it liked and tweaked them to make the game more friendly to solo players. At the time, the idea of doing something solo in an MMO was pretty nuts, and keeping people on the grind for as long as possible was the mission statement of the era.
WoW's model has been copied and iterated on a whole bunch since then. Many direct clones have fallen away, a few that innovated well have stuck around. The global standard, as you call it, is what's come out of that evolution. Things like actionbars, WASD-based movement, trackable quests, and solo leveling content.
Combat was not one of those things. Combat is actually something virtually everyone has done differently, each in their own way. WoW combat is not the same as GW2 combat is not the same as Secret World combat. They're all different, even if they did come from the same root (Everquest). XIV has its own style of combat too, a little on the slower side, but with an emphasis on skill combos and party dynamics (the limit break system here is unique in my experience). Could it do what it does better? Absolutely. And with time it very well might. But it's got a good beginning and a clear direction to grow in.