As a (mostly former) distance runner. Running endless marathons is most certainly not harmless. You will face eventually injuries which affect you for the rest of your life.
It is doing that for decades which messes you up eventually.
But my point is that you can run reasonably fast in races with fairly low running mileage. Do most of the base and tempo workouts cross training on an elliptical machine or something, and save the running for interval workouts.
True enough. I too have read "Born to Run", and would suggest that most modern humans aren't adapted to it (certain populations certainly, but most not). Although I have hit reasonably good times, I don't count myself among that population. In high school and in my 30's, I certainly was in the 90th percentile of runners, just by the numbers. Individual races, definitely higher. I love to look at the form and economy of top tier runners, and frankly, I'm not built like that; I could never perform like that. I'm bound to break down eventually, and I'm pretty good at running.
> on an elliptical machine or something
This is not running. This is training for running by not-running. Dress it up how you like, but it's how people like me save the damaging work for races.