I’m guessing we would have to ask the athletes themselves in order to suss out why they trained as they did, and why they changed.
For more naivety, could there possibly be a “best training” practice for different stages of an athlete – beginner, advanced, elite? As in, do world class athletes utilize POL because it works for world class athletes, where as a total beginner might be best served utilizing sweet spot methods, or vice versa, etc.
(My personal n=1 was winning a race after training 5 hrs/week exclusively in Threshold and VO2 (Z4/5), nothing else. Would doing another 20 hours/week of low intensity training (POL) or another 5 hours/week of Sweet Spot have made my victory more victorious? Why isn’t this a valid training method?)
Admittedly, I have not read every single post in this thread, but perhaps instead of just asking if X is better than Y, we might have to consider that there is no definitive answer and we need to ask who/what/when/where/why in order to arrive at the best type of training.