Space Seed could have been a two-parter

[FederationHistorian]

I thought Marla following Khan at all was a stretch. She betrays her oath and everyone she knows on the Enterprise for a person out of history? If they gender-flipped it and had a male crewmember betray his oath and ship for a historical female come to life, would that be believable? I don't think so.

TBF, we’ve never seen that happen before. There is no historical female with that kind of reputation in Star Trek. But as the Federation is a multispecies organization, it is possible some crewmembers might in fact do that for a member of their species.