No more absurd than assuming the opposite, a priori. In fact, it is more reasonable. Wherever there is data available for reason and senses to comprehend it is reasonable to assume the data is fashioned in such a way as to make itself accessible to comprehension and evaluation. Hence natural selection, mutations, and the like, are all manifestations of organized matter behaving according to predictable laws. I would expect this in an intelligently designed universe.
I've never doubted the presence of natural selection, mutations, new species, and the like. But I seriously doubt they account for all that is behind the history of the world as we know it. I also doubt their scientific usefulness.
The only thing the ancient astrologers recorded was the movement of the planets and stars.
They directly observed the movements of the planets and the stars, and they directly observed the behavior of people at the same time. They noticed recurring patterns of behavior at certain times of year and recorded that, too, over more than a thousand years of direct observation on the part of thousands of people. I would not be surprised if the foundations of astrology involved as much or more direct observation than Charles Darwin and all who have followed in his footsteps.