There are quite a few protestant theologians that would argue otherwise and do so pretty effectively.
There’s nothing in scripture that indicates the Petrine office, or even the apostolic office, was to continue past the deaths of the originals. Of course, I’m not hugely convinced by those arguments, but it’s not like scripture clearly contradicts them.
Then there’s the discussion concerning the powers and limitations of that theoretical head, if indeed it is supposed to exist.
Again, scripture is either silent or very vague on the issue.
With the Eastern Orthodox, there is no clear, visible head of the entirety of Orthodoxy.
Sure there is. Your bishop.
Each national Church has an incredible amount of autonomy, which decreases unity.
Over-vague, particularly as Thomas took the gospel east to Bactria and the Indus Valley and disappeared from western Christian history. I suppose he violated the implicit requirement to look Rome-ward (or Peter-ward)?
This lack of unity [in Orthodoxy]…
Again, this is just something you state axiomatically without having actually shown it. I observe tremendous unity in Orthodoxy. If I could be so bold, I think they consistently endure less clamor than their papist cousins.
also explains the fact that there is no Supreme Pontiff for the Orthodox, and thus they cannot be the Ark of Salvation, which must have one head.
I seem to recall the Ark of the Covenant having two seraphs upon it. Presumably both with heads intact. Just pointing that out
It is often customary, but not strictly necessary, for these things to be addressed in a Synod.
Which is the big rub. From an Orthodox perspective, no man is above council. No one can unilaterally alter what council declares save other council - not even a particularly influential bishop (say, of Rome).
To say that the Pope must consult with other bishops is characteristic of the error of conciliarism.
Yes, it was anathematized by the last ecumenical council (well… ecumenical to Catholics, anyway) before the protestant reformation.