We don't judge pop sci books based on what level of science they assume the reader has. There are myriad levels of understanding science. Every author must choose which level they feel comfortable condescending too. We do judge pop sci books based on the significance of what they are teaching. To me nothing is more significant to the layman than the answer to the question where we come from. Before the 70s we often thought that question was completely beyond science. Weinberg showed in the 70s that finally we actually could have some very precise info about where we come from. He explained that idea to the layman albeit to a layman who had done some very hard work in understanding science, nevertheless he put all the info together for a student of science to understand. For me, therefore, Weinberg deserves the laurels of having written the best pop sci book ever. Let's take another candidate for best pop sci book. Einstein wrote pop sci books. I know because I read them, albeit 12 years ago. Einstein told us that time and length were not exactly fixed. That's significant and pretty wild but it is not as significant as knowing the origin of the universe.