My assertion in this argument is (and this makes obvious sense) that people have different effort curves. I will use HR as a proxy for effort just to give it some quantification.
At 7:10 pace my HR is 130 after a few miles. At 5:30 pace, my HR is only like 20 bpm higher. SO I might be at a higher percent of my max HR at a slower pace than someone with equal race times but who insists 6:30 pace is easy, but each increase in speed doesn't take me as much closer to my max HR as it does theirs. So I have a gentler speed to effort curve and our curves intersect at some point below 6:30 pace. So I might be at 70% max HR at 7:10 pace while you have to run 6:30 pace to be at 70%, but I have to speed up alot more to increase at 1% increments. If I could draw on here, I would draw the graphs. This probably has to do with biomechanical physiology and how we train. This just makes physiological sense in the same way that we marvel at people who can run a decently fast marathon every few weeks, but whose PR's aren't as fast as you would expect. I just argue that for every person who has rightly found a relatively fast easy day pace based on an intuitive feel for an effort, there are 10 others forcing it based on these outliers.
Critique my training based on your "these easy runs are too slow" theory:
I am almost 41 and I live at altitude and just spent two years only running easy mileage and cycling because of sickness/surgery/further injury and have only been working out again for a month, so that puts the slow times in perspective, but this is my last few weeks of training.
All my easy road runs average in the 7:10-7:30 range. I am trying to go hard every 4th day. I always run the first mile of runs at 7:30-7:50 pace and generally don't have a mile at my average until 4 or 5 miles in. My workouts in the last few weeks (at 5000') have been:
1) 10 mile progression just to see how slow I had gotten starting at 7:20 pace and cutting down every half mile to 5:35 pace (with the last 7 miles averaging 5:46 pace)
2) 10 x 600m with 200m recovery in 1:55
3) 7 mile tempo in 5:38 pace with a :77 last 400m
4) 20 x 300m with 100m recovery in :54-:55 with 400m jog between sets of 5
5) 15 x 400m in :73-:74 with last 400m in :70
If I speed up my easy runs, I will either have to cut my 80 miles a week or slow down my workouts. Are you proposing I would race better of I slowed down my workouts to accommodate faster but still far, far from race pace easy runs? I mean, one has a quanta of energy to spend and a variety of ways to spend it, so if you add stress in one area, you have to decrease in another and the question is how best to spend that quanta to produce the fastest race times.
My long run last week was 15 miles with 5 on a trail at 8:30 pace and 10 on the roads at 7:07 pace and both parts were the same effort. Should avoid trails just because I can't run an arbitrarily determined acceptable pace?