Hodgie-san, what you say is correct, but your approach is too much influenced by the idea of marathon.
If it's true that the key is to work for enhancing the SPECIFIC ENDURANCE, the problem is to understand what SPECIFIC ENDURANCE means.
In the most part of the posts about Lydiard system, there is confusion between GENERAL RESISTANCE and SPECIFIC ENDURANCE.
The high mileage at slow pace has two goals only :
a) To increase the capillarization, but this works for short time only. In the first two years from the beginning of running, if we increase the mileage we arrive to FINISH the possibility of improvement in that direction. This is one of the big difference between a modern merhodology, and an old methodology (for example, Van Aaken), that supposed possible to continue in the capillarization for many years, every time running at slow pace. I remember Michel Jazy, already able to run 3'36" / 5' (WR) / 13'24", starting every year from 3 hourse at 5' per km. That's the reason because he ran "only" 13'24", while with a modern approach could be easily under 13'.
b) To be used as Regeneration, after fast workouts. Under this point of view, also today we use this methodology, BUT NOT LIKE TRAINING ABLE TO BUILD SOMETHING. One thing is to train FOR improving, another is to RECOVERY the real training.
So, the GENERAL RESISTANCE can be considered as the base for the SPECIAL ENDURANCE, and has a role only at the beginning of the activity (when you are very young), or, for short time, at the beginning of the season as introductive aerobic training, lasting no longer than 2 weeks.
Instead, we have to understand what the SPECIFIC ENDURANCE is.
Endurance is not a term with only one interpretation.
Every event needs Endurance, but this is the ability to extend your peculiar natural qualities. If you are a sprinter able running 10.0 in 100m, running 300m in 35.0 is ENDURANCE, running 1 hr slow is nothing, because there is no connection under the biomechanical and bioenergetic point of view.
This is the main point many people don't understand : they think that ENDURANCE means to run a lot of mileage, without giving importance to the INTENSITY of the endurance.
Another thing not clear is when people speak about HIGH MILEAGE. What does it mean high mileage ? Is 100 miles per week a high mileage ? For a 800m runner Fast type is not high, is damageous. For a 800m runner Resistant type can be ok. For a marathon runner is low mileage.
When somebody starts to think that THERE IS NOT A MILEAGE FOR RUNNERS, THERE IS NOT A SHAPE, THERE IS NOT A GLOBAL SYSTEM, but there are different specifisisms according to the athlete and the event, finally we start to live in a modern era for the training of middle distance, and we can finish to think that, for running fast, we need to use doping or some strange aid, because the performances are "out of the human possibilities".