What was the average number of minutes per week in Zone 3 or above?
The 80/20 notion comes from the “session goal” approach to quantifying volume. If an athlete had ten workouts in one week, and if the goal of two of those workouts was high-intensity, then the program would qualify as 80/20.
The problem with the session goal approach to volume is that it doesn’t account for the actual time spent in high-intensity training. When looking at high-level athlete training programs for long-duration events (i.e. like the marathon), actual minutes of training above aerobic threshold are in the neighborhood of 5%.
If you trained 80 hours over 14 weeks, you’d have an average volume of ~5h45′ per week. So to maintain your aerobic threshold, you wouldn’t want more than ~20 minutes of intensity for the week. To improve your aerobic threshold, you’d want less.
Actually quantifying the time spent at low and high intensities is described as a “modified session goal” approach.
With a long-term focus, I wouldn’t worry about your speed loss in the short-term. Improving your AeT now is where you’ll get the greatest benefit. I wouldn’t be surprised if, over the very long-term, your future AeT pace could be faster than your current AnT pace.