Interesting that Sargon, Henoch and Thalasia are mentioned. There's a brief exchange when Sargon talks about his people exploring the galaxy eons ago. He goes on to postulate that "your legends of an Adam and Eve may have been some of our explorers." Mulhall argues that life on Earth evolved independently. However, Spock cocks an eyebrow and observes, "That would however, explain some aspects of Vulcan pre-history." Later, when the three "essences" inhabit Kirk, Spock and Mulhall's bodies to construct their androids, Spock's body, already having a far greater heart rate, is not as adversely affected by the consentual "possession".
My point? Well, unless later material negated aspects of this episode, it seems to me that Sargon's race may have been the off world distant ancestors to the Vulcans and the business of Katras, carrying them in host bodies, depositing them within "vessels" (containers, not ships) is merely a continuation of what Sargon's people could do, merely "dolled up" in tradition, pomp and circumstance. At least, that's what came to mind when I say the "Search for Spock" three decades ago.
Sincerely,
Bill