I don't know that St. Augustine or St. Thomas Aquinas had any lack of belief in the Creator. Yet they made distinctions.
If they discriminated, they made mistakes. No surprise: Jesus Christ is the only Man Who never made a mistake.
As I said, I believe they were working on the knowledge that they had at the time. Science has increased our knowledge and our tools to demonstrate what is true.
(And, to prove that I can make - and admit - my own mistakes: That should have been, "before attempting to divide the image of God.)