Author/OP here. Just heard an interesting and relevant tidbit from someone who read the post. Apparently a while ago, Google fed resumes of employees into an ML model and correlated several metrics to the success of a specific engineer at Google. There was a lot of interesting data gathered from that but one that stood out was exactly that the number of certifications listed was inversely proportional to the engineer…
Do certifications inversely correlate with careers success, or do certifications inversely correlate with age? Older engineers probably don't have heaps of certs because they can fill a resume with prior experience. Additionally, Coursera/Udemy/edX and the like are relatively new and it's more likely that younger people would take more advantage of them. A junior engineer compensates lack of experience by using education and certs as evidence. The key part here is that older engineers are more likely to be senior, and by extension have "greater career success". That doesn't mean there's a direct correlation between certs and success.
I think there's a whole bunch of control variables to worry about before we could take anything meaningful from that data.