Actually, thing is, it's not that similar to FFXI. They reused the races, but past that, they seemed to intentionally do things differently than XI.
In the meantime, FFXI has undergone quite a number of changes over the years, much of which has served to make it a more appealing game. The current Abyssea content, in and of itself, is a vast departure from FFXI as originally released - albeit at the expense of the rest of the game, which is being largely ignored now as a result.
Either way, XIV would likely be a far better product if SE had actually taken their years of hard lessons learned with XI and applied them to XIV. If they -had- taken current XI and retooled it a little, put new graphics on it, then there'd be a lot more content, and a lot more tweaks already in place. They didn't.