FWIW:
"While many Orthodox theologians would say that not only the Bishop of Rome but all bishops are successors of Peter, yet most of them admit that the Bishop of Rome is Peter's successor in a special sense... the see of Rome also owed its primacy to the positon occupied by the city of Rome in the empire.. When hard pressed in the struggle against heretics, people felt that they could turn with confidence to the Pope…"
Timothy Ware "The Orthodox Church"
And the Popes in the first millennium professed the same Orthodox Faith we profess to this day, and many of them are Orthodox Saints.
Heresies reached, and most often sprang out of Constantinople, with the Imperial Patriarch as their chief architect. Satan managed to deceive the second only to the Pope, but the Popes never wavered (save for one possibly). We Orthodox have a lot to thank the Bishops of Rome.
For, such greats as +John Chrysostom and +Maximos the Confessor found refuge from heretical Patriarchs of Constantinople, and warm and brotherly welcome and encouragement among the Popes of Rome.