It is not as if Frank Shorter raced a sub-2:05 Marathon. No need to copy every thing he did. Training for the conditions one will face is good though. Shorter, used to warmer weather running was able to kick six different kinds of dog sh!t out of Bill Rodgers, 1976 Olympic Marathon. Rodgers was not prepared to race Marathon in warm weather that day in Montreal.
The best optimal mileage has already been established by Arthur Lydiard.
He recommended, if you were at the elite level, 100 miles per week in your main workouts
and then some easier, shorter runs adding up to about 6 miles per day.
That is about 140 miles per week if, and only if you can handle it.
Comparing running with skiing or cycling is like comparing baseball to football. All of them
are great sports but I wouldn't be going to the batting cage if I was a halfback or xc skiing if I wanted
to improve my pitching.
Swimmers don’t worry about being at altitude either. Again much higher training volume.