One of the things that badly hurt British middle distance running in the 90s and early 2000's was the obsession with 5 pace theory, running everything at good quality and not doing 'junk mileage' or high volume. That may work for some people but for many people especially if you more long distance based it is not effective.
Although Horwill did a massive amount for the sport in the UK setting up the British Milers club, coaching etc. I believe some of his ideas or possibly the misinterpretation of them resulted in a massive amount of harm to the quality of British distance running during that era. Probably the biggest single reason there was such a big decline.
I was brought up reading 'better training for distance runners' by Coe and also Horwills regular articles in Athletics weekly etc. and believing every run had to be hard. It's no wonder running 40-50 miles a week felt hard and I was always injured. Horwill was always going on about not running junk mileage and doing 12 mile long runs at half marathon pace etc. Most people brought up running in that era will tell you the same.
Jake's training seems more based around Horwill and Coes ideas. He runs all his runs fast and his mileage is relatively low. It has worked for him but I don't believe it works for the majority of people or for 5k or above. That way of training also carries a higher injury risk. As Jakob has shown you can approach 1500 from the other end of the spectrum in a less risky way. 5 pace training may work better for 8 15 types and Threshold focussed training for 15 / 5 k and above.
There is probably room for using five pace training when peaking alongside plenty of easy running after a big base of lots of Threshold work. I imagine that is not far off what Jakob does in the few weeks before a major champs. He mentioned recently in a interview that was the hardest thing to get right.