I’m not in agreement that is a bad example, however it might be taken out of context. This is what I’ve learned.
EF and decoupling are different metrics but related: Efficiency Factor and Decoupling | TrainingPeaks
Decoupling is a metric for seeing improvements to aerobic endurance during base. The article you linked has good information about that, and how to use on long intervals to determine when you’ve established good enough aerobic endurance to move from base to another phase of training.
EF is about how efficiently you generate aerobic power, which changes over the course of a season. Its the topic of this thread and in The Cyclist’s Training Bible there is a functional aerobic threshold test. Joe suggests doing this test every 3-4 weeks, year round. So EF is used to track aerobic fitness over a season. And in the article I linked, EF can even shed some light on short-term trends.
As Joe suggests, for aerobic fitness over an entire season you should track EF. Use decoupling during base to determine when you have established enough aerobic endurance to move into next phase of training.