Thanks for the ping. But aren't you being a little hard on poor Cyril? :) I mean, this was a man of God who had hands laid upon him. He was a direct successor to one of the Apostles, and carried great authority and great power for that reason. He rose to the rank of Patriarch. At the time, were his followers wrong to follow him? What should his followers have tested his teachings against, if anything? The Bible? Cyril would get an "A" there. How about the Eastern Church? Now here he would have failed of course, as proved out later.
I still cannot reconcile how you believe that God would instill all of these supernatural powers and authority to both the faithful and the heretic alike (God knowing all of this beforehand of course). I do not believe that Judas is the scapegoat answer because he was absolutely unique in the most important series of events. If Judas was meant to foreshadow following successors with supernatural powers, then the message is that we can trust no individual clergyman at all, only the collective will of the hierarchy. THAT would mean, especially in Orthodoxy, that the things we could be reasonably sure about would be relatively few. Is that a revealed faith?
There were more than one apostate bishop, starting with Marcion, Tertullian, and so on. There were also many an apostate Bishops of Constantinople, including Lucaris. Judas was an Apostle, yet Christ referred to him indirectly as the devil. Perhaps these people are there to test the faith, to challenge the Church. The Church is made up of sinners, FK, unless they are Reformed and God won't let them is no more.
BTW a Patriarch is not a "rank" but honor.
At the time, were his followers wrong to follow him?
Yes, of course they were. Obedience to a bishop is a given. But only if the bishop exercise economy (latitude within the doctrine), not if it is heretical.
What should his followers have tested his teachings against, if anything?
The whole wisdom of the Church: the scriptures, the patristic writings, the earliest documents, the Ecumenical Councils, hesychastic fathers...etc.
The Bible?
Have you ever read Philokalia volumes? They are laced with biblical references. There is no Church document that is not referenced to a Bible.
Cyril would get an "A" there
"A" for an apostate, yes.
How about the Eastern Church? Now here he would have failed of course, as proved out later
Not just the Eastern side of the Church, the whole Catholic and Apostolic Church.