M,
Matt’s not available to answer this directly, as he wrote the plans, but I think I can represent him on this topic.
Our 2020 Edition plans and earlier (which I wrote) did have a medium- and long-distance run. That’s the way I was educated as well, and it worked for our athletes.
Matt spent a summer training with a professional run team and noticed that they did not do a medium-distance run. They ran as you see in the Level 3 plan: consistently each day with a long run weekly. He noticed the same pattern with other elite runners He then re-wrote the plans accordingly.
I can’t empirically explain why, and I can’t even claim that it is better than the medium runs. What we can say is that this is the way the pros train, and that it has worked at least as well as the previous plans. I have full confidence in this new training method.
David