I have the FFX model viewer and I can explain how complicated Lulu's model was compared to the other playable characters in her own game in order to make her dress work. This is based off everyone's cutscene PS2 models.
Tidus: 217 bones 9749 polys
Yuna: 225 bones 9432 polys
Wakka: 218 bones 9177 polys
Auron: 243 bones 9484 polys
Kimahri: 232 bones 9035 polys
Rikku: 244 bones 9365 polys
Seymour: 238 bones 8266 polys
Lulu: 260 bones 9603 polys
Now, you can see here that Lulu has by far the most bones (animation rigging) and the second most polys after Tidus. She probably would have beat Tidus in both if she had feet or legs below the mid thigh

which she lacks because they would otherwise clip her belt skirt which as you can see here was it's own removed object from the rest of the dress on the modeling and rigging to help hide that they are just animating that section of the dress when she walks to convey her movement.

Here is a look at the belts too with the polys highlighted. Idk how to make gifs or I would, but the belts actually clip themselves all over the place just when she plain walks.
Her design is really interesting and SE's animators did a amazing job on her back in 2001. But this kind of design wouldn't fit well into FF XIV's design limitations and the need to make outfits at least partway work for a very diverse animation range for characters that have legs below the mid thigh.