I've always been torn about the "real" nature of the Romulan exodus. Spock mentions that he thinks that Sargon's people were in some way related to the Vulcans, which almost makes me think, in the grand scheme, that Vulcan and Romulus were both colonies of another, more ancient civilization that collapsed (which may or may not have been the same thing as the Preservers).
That's a fascinating theory. Here is the original quote:
SARGON: Because it is possible you are our descendants, Captain Kirk. Six thousand centuries ago, our vessels were colonising this galaxy, just as your own starships have now begun to explore that vastness. As you now leave your own seed on distant planets, so we left our seed behind us. ...
SPOCK: That would tend, however, to explain certain elements of Vulcan prehistory.
However, I tend to think that Spock was rather wondering how humanoid life developped on Vulcan in the first place.
It's correct, that Henoch insists that the Vulcan physiology is better capable of handling the stress of the merging, but that doesn't say that Sargon and company had pointed ears in their humanoid form, 600,000 years earlier.
I don't think the ancient Vulcan and Romulan headgear seen in both "Balance of Terror" and "Amok Time" is just a coincidental product of parallel development.