Nonparametric skew suffices in this case because nonparametric skew is what we’re trying to avoid. It is fundamentally unfair for districts to be drawn in such a way that as a whole the people of state could vote for one party in their state legislature by 8.5 points or more and yet have that legislative chamber controlled by the minority party. Yet the is precisely what happens in states like Virginia and Wisconsin. Reducing nonparametric skew deals with this problem, and drawing salamander shaped districts to achieve this is not fundamentally unfair.
The TLDR version of this is that the median seat controls the legislature so the median seat should reflect the state as whole for things to be fair.
Proportional representation may indeed be the bee’s knees, but it would require an amendment to the state constitution in many states. It’s not a practical solution in most cases. Redrawing district lines both through legislative efforts and through the courts is achievable. It’s what allowed the majority to finally take the the Virginia House of Delegates in 2019, and it’s what that same House of Delegates should try to further now that they have control so that the minority party can’t take back control in an election they lose by 4 points in the future.
Here’s a couple posts from an old thread about Wisconsin. The gist of them is that control of the Wisconsin legislature is extremely resistant to the will of the people. A statewide D + 8.5 win resulted in a legislature that is 36D to 63R. The median seat (and control of the legislature) won’t be in play unless an election is somewhere around D + 20.