I’ve engaged at length with Durston. Also Eric Holloway correctly explains that Durston is applying the exact same method he has put forward. Both Durston and @EricMH claim that FSC (that he calculates) is just an example of ASC. Look what Eric says about ASC (which FSC from Durston is an example):
That is exactly right. I entirely agree. However, Durston does not even try to formulate a P that takes into account common descent. That is his error. That means his estimate of is going to be much higher than it is supposed to be. He did not even test this with simulation. If he had, he would have found out that the vast majority of what he is measuring is the mutual information that arises from common descent.
Until Durston can produce a valid P, the FSC method fails. Even then, it still fails, as I have covered elsewhere. However just taking into account common descent is enough to explain the vast majority of information he is measuring.