The expansions released by Blizzard are just that, expansions. The magnitude of new content added far exceeds anything you would have found in FFXI. RoZ is the only offering for XI that even comes close....Everything since then is rehash of the same zones already available or re-skinned mobs.
WoW's expansions are just a level-cap increase, a handful of 2-hour instances, and a continent that I can plow through in 2-4 weeks. Treasures of Aht Uhrgan adds the same amount of content, just with jobs instead of level caps, and with interactive movies and forty-eight missions instead of walls of generic fantasy text. The following monsters were not re-skins, and were released as part of ToAU:
Colibri, Mamool Ja (several models), Lamia (several models), Trolls (several models), Qiqirn, Acrolith, Wamoura, Gears, Chariots, Wamouracampa, Flan, Automatons, Cerberus, Khimera, Hydra, Ramparts, Orobon, Poroggos, Marids, Apkallu, Dvergar, Imps, Soulflayers, Puks, Qutrub, Vampyrs, and
The re-skinned monsters are the generic species, like spiders, tigers, crawlers, and the like, that are added in as monsters of the environment and foster a sense of world cohesion.
The amount of detail put in to FFXI's monsters is astounding and, while they do use re-skins, they also add a staggering amount of unique and creative monsters as well. To say that FFXI's expansions consist of "already available or re-skinned mobs" is clearly untrue, as the above list (which isn't even an exhaustive one!) irrefutably demonstrates.