I disagree with your comments about the high middle ages not being a highly exegetical period. His main task as a university professor was to comment on Sacred Scripture.

Aquinas’ thoughts on the importance of the necessity of divine revelation even for natural theology are given in ST I q1 a1. He says “Even as regards those truths about God which human reason could have discovered, it was necessary that man should be taught by a divine revelation; because the truth about God such as reason could discover, would only be known by a few, and that after a long time, and with the admixture of many errors.” He discusses the problems of original sin on the human person. He would hardly advocate the idea that it is easy or common for the human person to even achieve a natural knowledge of God. When arguing about the possibility of natural revelation, he would say it’s possible, but not necessarily obtained without a great many helps. Moreover, Aquinas would advocate that the mind is direct to the truth by God as its first cause. Hence, in a natural way, one always requires God to know the truth. It seems to me to be unfair to decry Aquinas’ lack of appreciation for the effects of original sin.

In understanding St. Thomas, I think it would have been enlightening to discuss his engagement with his Patristic sources and the exitus-reditus pattern of the Summa Theologica.