Well perhaps an unspoken Catholic dictum is when in doubt regarding which Gregory wrote something, ascribe it to St. Gregory the Great.
However, St.Gregory Diologos was truly a good Patriarch of Rome, the most worthy man to hold that office since St. Clement. Most of the pre schism Roman Patriarchs with the exception of the odd villain like Victor, Honorius or in my biased Oriental opinion, Leo I, who dared to appropriate the Pagan title Pontifex Maximus, and in so doing IMO demeaned the Roman Patriarchate, were theologically conservative, thoroughly reliable figures, but only two spring to mind as exceptional leaders, Ss. Clement and Gregory Diologos. Most of the Fathers we venerate were either lay monastics or theologians, or the Bishops of relatively minor sees, with the Alexandrian Popes being somewhat disproportionately represented (Ss. Mark, Peter the Martyr, Alexander. Athanasius, Cyril, and for the OO, Dioscorus). Cappadocia was even more disproportionately represented. However St. Gregory Diologos was definitely a breakthrough leader; although I would disagree with him about Chalcedon and the role of his fourth century predecessor, every action he is recorded as doing I support. I love the probably apocryphal story of his encounter with Angle slaves that made him resolve to restore communication with the British church and evangelize the conquerors of the former British province. But there is much that he certainly did do that cannot be ascribed to mere hagiography that I think was superb.