The more I think about this the more I realize it is an issue of fundamentalism. Schiff is scrupulous in his reading of the score, and one can only commend that, but for other performances to be "wrong" is like saying every word in the Bible is literally true, and those that don't subscribe to every word are not Christians.
I didn't read the Pope's new book, "Jesus of Nazareth," but a review in Newsweek says that for many passages in the Gospel, the Pope doesn't consider it necessary to believe those events happened literally. Instead, the truth is found in meditation on what those events mean. I think it is much a similar situation: those old Romantic recordings from pianistic greats where the Moonlight is played slowly and atmospherically, contain a truth of their own, and the music wouldn't have been played like that for so many generations if it was totally false.
Even though Schiff is being as literal as possible, he is still applying personal value judgments. For instance his argument is based on what an appropriate "slow 2" feels to him. But Gould, to pick a name at random, was capable of feeling music much slower.
I'm sure I know exactly who on this forum is going to reply to this message, so everyone else please beat that person to the punch!
Walter Ramsey