Is the difference between raw and uncooked food basically the fact that cooked food has had its proteins denatured by the heat? Other than the development of gas bubbles or the absorption/loss of fluid, is there anything else going on with cooking, chemically-speaking?
All sorts of chemical reactions happen as you raise the temperatures of food, some good, some not. A good example of this is the Maillard reaction, which happens in all sorts of different cooking methods (but, notably, not the microwave, which accounts a great deal for the inferior flavor of a lot of microwaved foods). Carmelization also occurs with sugars when heated.
Some things don’t even change at all; they just warm up, because folks like them better that way. But many of those are pre-cooked.
Somewhat-related question:
One of the courses from the meal I talked about in this thread was “pancakes cooked tableside”. They were served cold after the batter was “cooked” on a slab of stainless steel that had been soaked in liquid nitrogen. While trying to explain the dish to my grandmother the other day I tried to compare it to “freezer burn” and also said something about how baking stuff had a lot to do with removing/steaming off moisture. That made a lot of sense to her (and it made a lot of sense to me as I was explaining it), but now that the OP talks about proteins I’m wondering if I lied to Gramma, which would just be wrong.
I think the other main consideration when cooking vegetables like potatoes that softens the material is the breakdown of the cellular structure (mainly starch and cellulose) allowing for easier (partial) digestion. This would involve swelling of any crystalline or dry starch regions and rupture of rigid cellulose cell walls by the hot water
The OP is completely wrong, so you don’t have to worry about anything he said.
Whether you were right is a whole nother issue.