I think some of the confusion is over what is low lactate and fat burning. The rest of the confusion is over periodization and specialization.
An aerobic endurance ride should engage both types of muscles (plus their variants) and there is lactate generated, perhaps blood lactate is as high as 1.7-2.0 mmol/L. The lactate generated by type 2 muscles should be oxidized and not too much spilled into the bloodstream.
I like the science as explained from Brooks and prefer to read. One could argue that there are only two zones.
https://www.sciencedirect.com/scienc...118301864#bib6