Honestly, an easy first step Cover can take to ensure problems like this don't happen again is to just stop working with Umiushi from here on out.
Fair enough if this was the first time they'd dropped the ball like this, then some leeway would be understandable; however, the fact is that this is now the FIFTH time Umiushi has put out substandard work like this, with other previous examples including:
Gura's default model having similarly stiff and jank rigging, although not quite as noticeable as her new model's is.
Anya's model having similarly stiff and jank rigging, along with the features on her head not doing the required perspective transformations when her head rotates. Also, Umiushi misinterpreted her design document and incorrectly added bigger boobs to her model. All of the above has culminated in Anya openly complained about her current model.
Coco's new years outfit and Matsuri's casual outfit both had similarly stiff movements and poor rigging, to the point where both girls wound up paying OUT OF THEIR OWN POCKETS to have Umiushi's awful work corrected.
Also, bear in mind that two other riggers, Jujube and Keffiy, were able to do the new outfit rigging of 6 separate talents (Jujube handling Calli, Towa, Kanata, and Ina's, with Keffiy handling Watame and Kiara's) in the same time it took Umiushi to put together this botch job, so clearly time was not an issue in this case.
Frankly, the fact that the same rigger has dropped the ball on multiple occasions with multiple talents' models - with this most recent instance being their most egregious, at that - simply indicates that said rigger's work is just not up to an acceptable standard, and as such Cover should stop working with them for the foreseeable future.
