The ninja relic isn't the only weapon with bits and pieces that look like they should animate randomly. Gea Bolg has this red pipe, strap, thing on it that, in production art, isn't so stiff in inflexible. And it's not just weapons, there's a fair bit of armor that has ribbons and skirts that animate stiffly, if at all, only because of heavy wind effects and walking. You apply finer animation to one thing then you have to do it for everything. It's this thinking that's kept Summoners from getting more summons until Heavensward.