Mgr Schneider is mistaken in believing that the pre-Pius X breviary was somehow "the breviary of all time" and that it remained unchanged after Gregory the Great. St. Pius V, for instance, altered the weekly "cursus" of the Psalter by moving some psalms from Matins to Prime. The balanced rationale for the Divino Afflatu reforms is explained in this Rorate Caeli article.

Dear Don Reto: That was my first question, too. But the office as Christ established it continues to exist, even though no one actually occupies, and the nature of the Church remains unchanged. See Appendix 4 of Traditionalists, Infallibility and the Pope. -- Fr. Cekada

To balance Salza and Siscoe's views, see Fr. Cekada's Stuck in a Rut: Anti-Sedevacantism in the Age of Bergoglio and his Why Are Traditionalists Afraid of Sedevacantism?