I think there’s some confusion about the typical zone definitions. I haven’t read the article, but in most five-zone frameworks, “under AeT” means zones 1 and 2 while “over AnT” means zones 4 and 5. In that context, it would be zone 3, not zone 2, that is to be avoided minimized.

The reality is that zone 3 is useful, but too often over-emphasized and over-used (because it’s gratifying and most people confuse effort and gratification with progress.)

An effective approach would be to use a largely polarized model early in a macrocycle and then include the appropriate amount of zone 3 close to a goal event. As suggested, “appropriate” is often over-estimated.

Polarised training with Stephen Seiler, PhD | EP#177

That makes sense and fits with the UA perspective (and most professional endurance athletes.)

Current zone systems grew out of a three-zone model where ventilatory thresholds (VT1 and VT2) marked the bottom and top of Zone 2 in a three-zone system (and corresponding to AeT and AnT, respectively.)

Later on, Zones 1 and 3 were split into 1/2 and 4/5, respectively. So Zone 2 in a three-zone model corresponds to Zone 3 in a five-zone model.