This is a fairly absurd argument in several ways.
It appears that you do not contest any of Cain's accusations towards Salazar and the NOP as a basis for your view. Instead your basis is that Mary Cain chose to be coached by Salazar?
Cain choosing to be coached by Salazar does not give Salazar the green light to be abusive. Choosing to marry someone does not give the other person the right to be abusive towards you. More generally speaking, choosing to associate with another human being does not give that human being the right to behave abusively towards you. If that is something you believe then I feel very sorry for the students you coach if you are indeed a coach.
Of course women are not going to magically appear out of nowhere as coaches. You say "for whatever reason" women are not interested in getting into coaching. It appears that Cain's story presents a fairly good reason why that might be the case!
There is plenty of evidence that people do not perceive women to be as effective coaches across sports because they are not as fast as men. This is almost certainly not the case. Unconscious bias leads people to make decisions, which are not necessarily rational.
Between a former female olympic marathon champion and a former male olympic marathon champion, the vast majority of men and many women would probably prefer to be coached by the man even if there is evidence to suggest that the woman is the superior coach.
These types of behavioral biases are persistent and create systems and feedback loops, which leads to the kind of toxicity that Cain described in her NYT op-ed. Add on top of that to the fact that the men who are at the top of the sport at all levels won't want to give up their spot and women are going to have a tough time breaking in even if they do show interest.
Of course that toxicity won't be solved overnight. Of course women are not going to suddenly make up half of all coaches. But it seems clear that in order for this toxicity to be solved, women will have to have a substantial say in the shaping of this sport.
I applaud Mary's efforts to make running an honest sport in this country that we can be all be proud of from the pros to the high school jv squad.
It's not like Salazar or anyone else at the top of the sport is doing much to systematically improve the ethical practices for running in this country.