Max, you're not making much sense right now.
In many places of the world, a precedent is the primary tool in, say, passing a sentence. In fact, you can use it yourself in this game when passing judgement.
None of those compare to elections. A mage can't become Divine. A politician becomes Divine. The fact that they have magic is irrelevant. They don't make popular choices, they'll never be Divine. I don't see why you would think otherwise. Anything a mage Divine could possibly be elected over, would happen anyway. Unlike Vivienne, they won't have the Inquisitor backing them up.
Having a mage as Divine of course sets a precedente. And there is always the possiblity of it being exploited at a later date.
That does not mean that every mage has a chance any more than every woman has of becoming the Divine. But by allowing one mage to do so, you lift the restriction that previously forbid them.
I do not get the logic behind this. Divines are elected. By mundanes. Who care about what powers said person being elected has? If the people don't want to elect them, they won't. This is like saying because John F Kennedy was Catholic, there is no a precedent for Catholic presidents. I'll go ahead and tell you that isn't true. Who cares if a mage is Divine? She wouldn't gain that position unless she had policies others would want her to enact anyway. There was never a mage restriction on Divines anyway, just like there isn't one on male Divines. It just doesn't happen because no one wants it to. You're acting like we slashed a few rules from the book when this happens.
Also, if playing as a man you ask Cassandra herself why you can't be Divine, she'll tell you that making a man Divine would be the equivalent of surrendering to Tevinter.
Hence why it's strange men are an absolute "NO" but a female mage can be an option.
You do realise what that sentence means yes? It does not mean what you think it does. It means no one wants to make a man Divine anymore than they want to go back to being magically oppressed, which by the way, in case you throw that out as something that would happen with a mage Divine, would not even be possible under Vivienne or any other mage, anymore than any Divine before her was able to dominate. That is to say not at all. If the people, and more importantly the church, don't want to go along with it, it won't happen. That simple, really.