There seem to be largely 2 camps on easy runs
- short, only moderately slow easy runs, may do more workouts per weeks than the other camp. Running too slow is useless
- longer, slower easy runs. Try to get the most mileage they can, with roughly 80% of it easy, possibly more at certain points of the year. They may do progressive runs and finish as fast or faster than the other camp every now and then.
Taken to the extreme the short camp is only doing like 5-6 mile runs on easy days, 6 runs a week, and a lot of intervals/fast intervals on other days. The extreme for the higher mileage slower easy runs group is 160+ mpw or triples.
Some runners could succeed in either group, others would not run well after training under one of the approaches.
We need to stop pretending there is one right way for everyone, one formula and realize training should be individualized. The most successful coaches find the sweet spot for any given athlete.