Yet More Evidence that PRS is Largely a Measure of Population Stratification

Here is another study pointing to the lack of validity of polygenic risk scores.  This one was for height:

We find that the signals of selection using UKB effect-size estimates for height are strongly attenuated or absent. We also provide evidence that previous analyses were confounded by population stratification Therefore, the conclusion of strong polygenic adaptation now lacks support. 

If you aren't able to control for population stratification for something as straight-forward and quantifiable as height, then certainly you won't be able to do better with "Educational Attainment" or really any more complex psychiatric trait or mental construct.  The null here, is that polygenic scores largely measure population stratification and I would be interested in what could be demonstrated that would lead one to reject the null.  Moreover, the failure of PRS also brings into question the polygenic (and, presumably omnigenic) models for phenotypes.