Of course Schumaker doesn't focus on running form, he recruited the best in the nation at Wisconsin and now coaches the best at the elite level.... but oh wait, how long as Tegenkamp been injured? How successful was he with Matt Withrow?
He gets to work with elite runners and there's good evidence that runners who make it to that level had good running mechanics in the first place (American runners not being as superior as a high number of east African elite distance runners when it comes to form).
But, could he take a team of injured high school runners and get them running high mileage, uninjured with no focus on form? Most likely not. You would send them off to PT's and doctors.
By focusing of form, you can get people running high, uninterrupted mileage with no injuries. I've done it and had a group of injured kids go from 5:00-6:00 miles to 4:15 to 4:35 miles in a seven month period of time. High mileage and AT development did work, but only because they were injury free and focusing on economy of motion.
Yes, running is the best way to improve at running, but focusing on the WAY you move while running rather than solely the physiological gains is a more complete strategy.
Or, you can just cherry pick and thrown a dozen eggs against a wall and rest your laurels on the runners that come back uninjured/eggs unsmashed, as do most coaches. What was the injury rate of Wisconsin's runners during Schumacher's years? How much better could they have been with no injuries? Has he every coached a team that had absolutely no injuries for a complete year at the collegiate or post-collegiate level?
In running, you have Economy, Vo2max, Anaerobic Threshold and Aerobic Threshold and I put Economy first.
Saying to only focus on the physiological adaptations of running and not THE MOVEMENT THAT IS RUNNING is not working for too many people to continue saying that by just running, your form will get better. You can take a square stone, roll it for a long enough period of time and yes, the corners will round off, but it will crack in half long before it becomes a perfect circle.
We spend months upon months before the age of 2 years old learning how to move in a bipedal manner. That is a serious amount of time dedicated to learning how to move. It is a skill. We stop running and then try to pick it up later and we have lost the skill. If you compare the mechanics of any 20 month old child on any continent to another, you will see little deviation from one to the other. If you compare these children's mechanics to the best African runners, you would still see little deviation because the elite African runners reinforced the mechanics and the skill they learned at a young age. If we compared these children's mechanics to American runners, we would see a huge deviation in the way they move vs. the way we move and this is the underlying difference in performance between African and American runners.