One of the best high school coaches in Washington state way back in my day was supposedly an ex pole vaulter who never ran. My coach was a long distance school record holder at UW and had me doing less than 30 mpw as a senior. The pole vaulter's guys had far better results and I believe he's in the WA high school coaching hall of fame.
Regarding Jack Daniels, he was a two-time Olympic medalist in the modern pentathlon, which of course has cross country as one of the events.
I don't think a PhD is necessary to coach well. If you are able to digest the findings of PhDs and apply that to coaching, you don't need to be a scientist yourself.
I work in "field engineering". Essentially our factory engineers design products and ship them out to the military to be used in their operations. Out in the field, where the products are being used, we install the products, upgrade them, advise the military of their limitations and capabilities (they often want to do new things that may or may not be possible with the products they have, or may require upgrades), repair the products, etc. The factory engineers don't have the first clue how to work in the field, and quite often we find major design flaws or limitations that have found their way into the product and have to let the factory know their product is faulty. If I went back to the factory, I would have only the faintest idea of what I was doing regarding design in any of the engineering areas within our products, but have the background to learn it if I needed to. Most frequently when field engineers move into the factory they become system engineers because we're generalists who know how all the parts interact with each other. Design/theory vs practical application are two completely different arts.
I see great coaches as physiology field engineers; they take all the specific knowledge generated by PhDs and implement it into a training program that works. They know how to deal with diverse things like an athlete's mental issues, the 1000 things that can go wrong at a meet and how to best deal with it, when to abort a workout when it's going bad, etc. This can only come from a lot of experience, which might have been gained while one was competing themselves, or through years of coaching. Someone like Jack Daniels could be both a successful researcher and great coach if they took the time to work in both fields.