So after reading half of His Broken Body (in 3 days), it seems as though Theodore the Studite was a "proto"-eastern Catholic. In other words, he seemed to have supported the Papacy more than other Greek Fathers. Is that a fair statement?
No. One must look at the context and history, as well as take non-Orthodox books with a grain of salt. St. Theodore was a fan of the Roman pope because, at that time, the Roman pope was Orthodox. Also, he was the one voice of Orthodoxy in the non-Islamic sphere. (Not sure about Antioch, whether at the time it was ruled by the Mohammedans or the Eastern Romans.) The Patriarch of Constantinople, if he were Orthodox, was deposed by the Iconoclastic emperor.