re: Not how heat shields have to work.
The point is you are managing the heat in some way.
A pressure suit needs to be light weight and mobile. The things they are talking about wouldn't provide this at all.
You try to come up with liquid cooling that works and see the actual requirements. On a jump that they suggest you would need a heat shield for the very reasons you state.
Here is Kittinger in 300 pounds of equipment. He was jumping at a much lower altitude and was dealing with cold...