I'm more than a month late but thought I should chime in on this one.
At least to my knowledge model animations are not entirely animation schedules (the way they were in FFXI). By this I mean stuff that is technically "loose" such as cloth straps, hair, flaps in clothing and so on had their own animations to simulate physics without actually having any in the game. This is why they had slightly more freedom with body shapes (female elvaan and their bountiful derrieres come to mind...).
ARR's engine seems to be a mix of animation schedules (for movement like walking, running, strafing, casting animations) and physics (for hair and clothing). The main problem is that round surfaces + physics are very system intensive, and can be difficult to get right using minimalistic approaches like decreasing poly count of models. I'd know because I've been tinkering with dat mods (nowhere near to godlike entities like Mooshywooshy) and FFXI models for MMD. Part of getting the physics right involves, as you may have guessed, removing some of the roundness from the backsides of characters when called for.
I'll admit, this is just based on what little experience I have tinkering with models. I don't know the details of ARRs engine nor did I go to school for computer animation. I will say cutting the "fat" is faster and easier to put together, so I can believe Suzuki-san when he says it was done to save themselves time and money.