In the East the relation between the Empire and the Church became what is known among scholars as the "Byzantine Symphony of Powers". One Emperor put it "I have charge of men's bodies, the Church has charge of their souls": the two represented distinct but cooperative sources of authority and power in the society of the Christian Empire. Each had its own proper sphere of operation, and each had a role in restraining or guiding the other: Bishops and the pious faithful often rebuked Emperors who fell into excesses (although they sometimes got themselves exiled, or even martyred if the Emperor was particularly bad--these are often commemorated on our calendar of saints, while clerics who supinely went along with Emperors who strayed from the faith are reviled in our histories). Emperors intervened in the Church from time-to-time, but the interventions which stuck (the councils we now recognize as Ecumenical Councils) were always for the peace of the Church in time of ecclesiatical termoil, and didn't try to enforce an outcome to the Emperor's liking (well, with the possible exception of the Seventh, which the Empress Irene called to undo years of imperial meddling by the iconoclasts, to restore traditional piety).
Inevitably when Emperors meddled in theology rather than intervening for the good of the Church, their work soon undone by the Church (the "Henoticon" of Emperor Zeno, the iconoclastic movement, and the False Union Councils come to mind). Likewise, seldom did interventions by hierarchs in properly political matters, as opposed to moral matters, ever have a lasting or salutory effect on either Church or Empire.
That's an interesting way to put it. Tell me, who/what "scholar/s" did you quote it from? BTW did the discussion about Pope John VIII and Photius ever go anywhere? (I'm sorry I haven't been able to follow the thread this weekend, but I was interested in it)