Well, Bowler, it's somewhat amusing that you blithely dismiss so easily a ramification of what you were just insisting upon in another thread, though you didn't realize this was a consequence of it. Namely that the Church is spotless.
Pope Pius XII says of the Church, the bride of Christ, "Certainly the loving Mother is spotless in the Sacraments" which at a minimum requires they not be invalid.
She is holy by her sacraments, this is why she is not tainted by the sins of her children and remains holy in her nature and essence, for her sacraments and their validity are not affected by these, even when her children sin, fail and fall repeatedly and terribly.
Like I said, if Davies was writing for a sedevacantist audience, he would have contended himself with other arguments such as I mentioned above. But he was not.