Econometic methods take one variable at a time to estimate an equation for testing.
You have absolutely no idea what you're talking about. Have you ever even read an empirical economics paper published in a reputable journal? Just try submitting a paper with with a single variable equation, and the referee will laugh in your face.
Do me a favor, pick up an econometrics book and look up the terms "omitted variable bias" and "spurious correlation."
Econometric equations with one independent variable were used during the infancy of the science. How did you get the idea that I claimed one would satisfy the referees at Econometrica today?
When deciding on explanations for an economic change it is usual practice to add one variable at a time to the equation. You don't just throw in everything you can think of into a regression estimation.
As anyone who has looked at the classic Lawrence Klein -An Introduction to Econometrics would know the very first equation discussed used one independent variable. It is standard to start with one and look for more when its correlation is not sufficiently high. Advanced econometric models use many.
While it has been 30 years since I took an econometrics course the terms you refer me to have no obvious relation to what I was discussing. Tests for spurious correlation are available but that was not at issue. Autocorrelation can also be detected and accommodated. Even heteroscedasticity.