Just because something is not conclusive does not mean it is not research. Research can be conclusive or not conclusive but it does not change the fact that it is still research. I agree that some research is better setup and structured than others and you can have more confidence in the conclusions.
But based on your explanation if something is not 100% conclusive, which as you said 'it is impossible to correctly isolate Google in order to come up with valid research', then we should never be doing any research in SEO. If we are not doing any research then we are observing things and trying to come to conclusions (which technically is research) which is exactly what seoreel did in their article.
As I have said numerous time seoreel was not testing this, it was an observation they found, so I do not understand what you are arguing about.
We can test things and find techniques that appear to work, but it is impossible to isolate any single variable to determine if that is the cause why something works. Over time we identify certain things that appear to improve SEO rankings and results, but we can never know for sure that it is that one technique alone that is improving the results or if it is a combination of things.
The key is to analyze each technique and theory on its own merit compared to your own experience and knowledge. Many theories fail this test, and some may appear to work or be useful on first glance but over time are exposed for the sham they are.