Abraham's True Sons, Alexandria's True Bishops

The other day I was directed to a fascinating discussion on the Puritan Board (which I've subsequently joined) on the topic of Sola Scriptura. The thread was started because one of the members was being challenged by a friend who had been investigating Catholic and Orthodox theology and began challenging him about whether the Bible and the early church fathers teach that Scripture is the believer's sole authority on matters of doctrine and practice.

Here's the thread: http://www.puritanboard.com/f121/sola-scriptura-scriptural-50212/

Now, as I read the various responses (some characterized by heat, others by light), I did notice a fair bit of straw-man argumentation. But fallacies aside, there were also a lot of quotes from church fathers that seem to indicate that true apostolic succession is what Protestants say it is, namely, a succession primarily of doctrine, with the issue of physical, laying-on-of-hands succession being a matter of historical coincidence and nothing more. Consider this quote from Gregory of Nazianzus (330-389):

Thus, and for these reasons, by the vote of the whole people, not in the evil fashion which has since prevailed, nor by means of bloodshed and oppression, but in an apostolic and spiritual manner, he is led up to the throne of Saint Mark, to succeed him in piety, no less than in office; in the latter indeed at a great distance from him, in the former, which is the genuine right of succession, following him closely. For unity in doctrine deserves unity in office; and a rival teacher sets up a rival throne; the one is a successor in reality, the other but in name. For it is not the intruder, but he whose rights are intruded upon, who is the successor, not the lawbreaker, but the lawfully appointed, not the man of contrary opinions, but the man of the same faith; if this is not what we mean by successor, he succeeds in the same sense as disease to health, darkness to light, storm to calm, and frenzy to sound sense. NPNF2: Vol. VII, Oration XXI - On the Great Athanasius, bishop of Alexandria, §8.

Gregory seems to be saying that "the genuine right of succession" is rooted in a bishop's piety, without which he, though enjoying literal apostolic succession, is "only a successor in name." One is reminded of the argument both of Jesus and Paul that Abraham's true succession of children is traced not through physical lineage but through something not quite as visible, but nonetheless ar more important, namely faith.

Thoughts?