I agree we are all an experiment of one. I’m a long time runner who found cycling through injury. I coached track/XC which included coaching my daughter through this timeframe up until she ran in college.
As mentioned above, Parker Valby trains with low running volume due to injury risk. There are many other females who do the same with great success. On a personal note, my daughter began including cycling into her running program (reduced running volume). In a year, she went from 19:22/5k to 17:59/5k in XC. I was her coach and the only key variable that changed was the reduction in running volume and increase in cycling volume. Of course, she aged a year.
Often you will hear of female athletes training in this manner due to repeated injuries. Due to low body fat levels and training, the female athletes have amenorrhea which can lead to estrogen deficiency and negatively affect bone mass. My daughter and two of her roommates/teammates all had this and were diagnosed as having low bone density. They were at high risk of stress fractures. Training in the above manner is a necessity, but not all coaches adhere to this and the athletes continually “break” and the athletes leave the sport.
I’m out of coaching, for now, but if the time comes, I will train athletes to include more cross training. I do think volume is important, but being a complete, healthy athlete is also important. 