Ceteris paribus, or all things equal is a super common economics phrase. It’s basically impossible to maintain in the real world. Economics used to be considered philosophy for a reason. As someone with a economics degree I do pretty much agree with you.
The “hard science” part of it is using past data to build models. You’re still more or less trying to tie the figures into a theory of why they happened that may or may not be true. There are so many factors it’s impossible to know. For instance I truly believe that the stronger anti-monopoly enforcement and higher taxes played a major role in America’s success and the rise of the middle class from post WW2-80s. I have to admit that there are an insane amount of other factors at play here that might invalidate all the trends during the same time though. Every other developed countries info structure being bombed to the ground giving the US a huge start not being the least of which.