I witness now before God and men, they have torn themselves away from the Body of Christ, from the Surpreme See (Rome), in which Christ placed the keys of the Faith, against which the gates of hell (I mean the mouth of heretics) have not prevailed, and never will until the Consummation, according to the promise of Him Who cannot lie. Let the blessed and Apostolic Paschal (Pope St. Paschal I) rejoice therefore, for he has fulfilled the work of Peter.(Theodore Bk. II. Ep. 63).<quoted text>The Studite is legitimate.Keep in mind that the monastic order he founded are Eastern Catholics today, not Eastern Orthodox. If the Eastern Catholic existed when the Studite lived he very likely would have been Eastern Catholic, therefor not representative of Orthodox on the Pope issue. Theodore the Studite is loved by the Orthodox for his defense of the icons.
Was St. Theodore a heretic?