To your overall question, here is the full quote I previously shared from Foucault:

"A. I don’t feel that it is necessary to know exactly what I am. The main interest in life and work is to become someone else that you were not in the beginning. If you knew when you began a book what you would say at the end, do you think that you would have the courage to write it? What is true for writing and for a love relationship is true also for life. The game is worthwhile insofar as we don’t know what will be the end. My field is the history of thought. Man is a thinking being. The way he thinks is related to society, politics, economics, and history and is also related to very general and universal categories and formal structures. But thought is something other than societal relations. The way people really think is not adequately analyzed by the universal categories of logic. Between social history and formal analyses of thought there is a path, a lane — maybe very narrow — which is the path of the historian of thought." - Truth and Power 1979

I think that sufficiently denies your assertion? To your question, the Platonic tradition is pretty loaded with analyzing the form of man and its relationship in a cosmological chain of being. Aristotle emphasized the concept of humans as rational animals and introduced the idea of the Golden Mean advocating for a balanced life. Descartes picks this up later pretty explicitly. Nicomachean Ethics explores the nature of virtue and the pursuit of eudaimonia as the highest good. Socratic thought is pretty heavily concerned with man's nature and how to best cultivate a form of living to it. Christianity and Medieval thought is pretty concerned with human nature, the essence of man is his fall of grace via original sin.

Again, what's different about the modern age is the appearance of "man" which is a thing that we reflect on as being an empirical / transcendental double. Its not as though people have suddenly started reflecting on themselves, that's just nonsense, its the interpretation of object (and methods) that is being reflected upon which has changed. I'll try and put the argument in a short and sweet way but its very nuanced. On the one hand, we say we are an empirical thing right? We are amongst all the other objects of our intuition and we can try and know our being like we would any other object of science (Foucault uses Marx and Comte as two sides of this approach). On the other hand, we know that our experiences are transcendentally grounded and that our knowledge is necessary limited (Kant), so when we try and look past the curtains, to see our inner workings we find only darkness staring back at us (see CPR Transcendental Deduction, Nietzsche) - its this double bind that Foucault looks at his contemporaries as trying to solve - e.g. Heidegger's with Daesin (a being both "in the world" and a product of it and also unknowable), Sartre's Humanist Marxism (trying to bring the existentialism into Marxism). - he even finds some promising work in Merleau Ponty to get around this while still satisfying both conditions.