The problem is in the buttocks. This short skirt should have all geometry assigned to the hip (and maybe abdomen). Thatl'll give you smoother deformations.
If you want longer skirts to behave, you have two options.

1. Dynamic or conforming/dynamic hybrid. Dynamic parts work very well for skirts.
2. Don't use the buttocks/thighs/shins. Instead, create "rings" of polygons and create a chain of bones originating from the hip, going straight down, matching the "rings".
   This kind of skirt does not automatically fit the legs, but is fairly easy to pose.

The pen is mightier than the sword. But if you literally want to have some impact, use a typewriter

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