FFXI doesn't need close to those 100 buttons, just as you don't need the analog sticks. People play with gamepads just fine, as it was designed for one - and because it feels better, it is better (IMO of course, as posting on this forum is for). If we were talking about a game that was designed for keyboard in mind, of course it would be superior. But there is no way I can play a console port (which is what FFXI is tbh) with a keyboard + mouse over a gamepad. Even those with good kb+m controls like Saints Row 3 I still use gamepad over.
And FFXI is in no way a first person game - it's a 3rd person MMORPG. Just because you can zoom in first person doesn't doesn't classify it as a first person game that keyboard/mouse is more suited too, it's entirely different.