When did I say that any of them were slow twitch? I said that we all have natural inclinations based on the distribution of muscle fibers that we're born with. Of course they're not getting biopsies, but you don't need a biopsy to know whether someone's strengths lie in natural speed or endurance -- it's pretty obvious by their performances which way they lean.
When did I say that speed was not important? Why do you think that speed development and aerobic development are mutually exclusive? They're not. They both have to be developed from a young age.
I never said that Grant fisher was slow twitch, nor did I say he was fast twitch. He had sub 50 second 400m speed in high school. He also didn't run 70 miles per week, he ran 50, like I said earlier. He ran the mile in high school but gravitated towards the 5k in college and as a pro because that's obviously his better distance. He runs the event he has the greatest chance for success in.
Webb broke 1:46 in the 800m once in his life. Where would that get him? He worked on speed so much throughout his career, yet he would tell you himself he just didn't have great top end speed. He's said it before in interviews. You can DM him on instagram and ask if you want. He was able to hold a high percentage of his max speed for a long duration and that's why he was good at the 1500 and even the 10k. You can't hold speed without endurance.
Low mileage isn't the only way to run the 800m, nor is it the best for people that want to succeed at distances besides the 800m. There are many highly successful 800m runners that ran/run high mileage. Coe and Ovett both ran 100 miles a week at times. Coe lied about running low mileage to mess with his competitors. The contribution of energy via aerobic pathways accounts for 60% or more of the demands of the 800m -- it's hugely important. I'm not saying that high mileage is a requirement, just that aerobic development is.