I see what you’re saying, I noticed similar things in my youth. As I studied more though, I realized I was simply cherry-picking, and filling in the gaps with pop culture misconceptions.

The plateaus and valleys you describe, for instance, are some of these misconceptions, stemming from old schools of thought. Modern scholarship points how how progress in many arenas continued through the dark ages and medieval period. You could look at the history of something like military fortifications and see this progress very clearly, in a situation where we have a great many old examples to study.

Regarding this social oscillation you describe, I think it’s fairly cherry picked. With the whole data set, this starts to become more clear. How about the history of Denmark or the UK? How about Chinese or Japanese history? These will all break your hypothesis.