When the show started it and it was entirely biological it made a kind of sense. But as it went on and it became a cultural thing it made less and less.
Interesting idea. It's almost like TOS treated logic as a inherited trait:
(From TOS All Our Yesterdays):
MCCOY: Are you trying to kill me, Spock? Is that what you really want? Think. What are you feeling? Rage? Jealousy? Have you ever had those feelings before?
SPOCK: This is impossible. Impossible. I am a Vulcan.
MCCOY: The Vulcan you knew won't exist for another five thousand years. Think, man. What's happening on your planet right now, this very moment?
SPOCK: My ancestors are barbarians. Warlike barbarians.
MCCOY: Who nearly killed themselves off with their own passions. Spock, you're reverting into your ancestors five thousand years before you were born!
Except, Spock still displays emotion:
(From TOS The Savage Curtain)
SURAK: Live long and prosper, Spock. May you also, Captain Kirk.
SPOCK: It is not logical that you are Surak. There is no fact, extrapolation of fact or theory, which would make possible.
SURAK: Whatever I am, would it harm you to give response?
SPOCK: Live long and prosper, image of Surak, father of all we now hold true.
SURAK: The image of Surak read in your face what is in your mind, Spock.
SPOCK: As I turned and my eyes beheld you, I displayed emotion. I beg forgiveness.
SURAK: The cause was more than sufficient. Let us speak no further of it. In my time, we knew not of Earth men. I am pleased to see that we have differences. May we together become greater than the sum of both of us.
Now here it sounds a bit more cultural.
Later on, in the same episode:
SPOCK: You had no choice, Captain. You could not have stopped him.
KIRK: How can you ignore that?
SPOCK: A Vulcan would not cry out so.
KIRK: Whether he's a Vulcan or not, he's in agony.
SPOCK: I am not insensitive to it, Captain.
Again, an acknowledgement that he is feeling something for Surak.
And in Journey to Babel:
SPOCK: Mother, how can you have lived on Vulcan so long, married a Vulcan, raised a son on Vulcan, without understanding what it means to be a Vulcan?
AMANDA: If this is what it means, I don't want to know.
SPOCK:
It means to adopt a philosophy, a way of life, which is logical and beneficial. We cannot disregard that philosophy merely for personal gain, no matter how important that gain might be.
AMANDA: Nothing is as important as your father's life.
SPOCK: Can you imagine what my father would say if I were to agree, if I were to give up command of this vessel, jeopardise hundreds of lives, risk interplanetary war, all for the life of one person?
Again, hints at cultural.
So, it appears that even TOS had elements of both.