30-40 mpw is pretty normal for speed-based 800 runners. Brazier was only running 20 mpw under the Texas A&M coaches IIRC, so this would be a bump up for him, and I believe I also recall Rudisha saying that he ran his world record off of less than 40 most weeks. There are multiple valid ways to train for the 800, an endurance guy like Nick Symmonds might be better served off of 60-70 mpw, but there's no need for athletes with more of a 400 background to be doing that much mileage. Brazier can build the endurance that he needs to handle the rounds off of longer interval sessions, and by not running high mileage, he is able to stack a greater number of quality workouts. The fact that he was still able to run 3:37 without training like a miler shows just how talented he is.
All well stated, he has insane youth on his side too, only being 22 years old, you're firing on all cylinders and then some, factor in alien genetics and you have well..Donovan Brazier