It has already been decided that the AI will not be able to reach the Galactic stage before you, therefore it is impossible for the AI to Ascend before you manage to leave your solar system, there for your arguments to the first three points are null and void.
If my suggestion for having a difficulty setting in which the AI surpassing you means death the next turn, then by all means, play the way you want to play, but according to the Official Wiki (What is Thrive) going auto extinct because the AI surpassed you will NOT be a thing, Hhyyrylainen has acknowledged this, and even if my suggestion to meet in the middle with difficulty setting gets accepted, in 2 of 3, your statement remains completely invalidated.
Though I agree with your statements about 4 and 5.