I ran cross country and track for Mr. Newton (85-88). I was a group 1 runner but due to injury and a bad couple races towards the end of the season, didn't get to run the state meet. I did have two brothers who also ran for York and weren't close to the top 7 and never ran in groups 1, 2 or maybe even 3.
The program has had an unbelievable amount of success but what really makes Mr. Newton special is how he motivated so many kids to do their best and to believe in themselves and the team. What also makes the program stand out is that almost invariably, some of the worst, least talented runners end up making or being near the top 7. Part of that reason is the high mileage and tough workouts that give everyone the opportunity to develop over 4 years. The success and high profile of the team may bring numbers to the team but how the coach motivates the team and camaraderie we shared is why runners stick with it despite all the hard work.
But with so many kids joining the team, and to your point about how their workouts are managed, it's not as extreme as some might think. I don't remember the exact mileage we ran but certainly not everyone ran the mileage that group 1 did. Most of the miles we put in were by time and not by set distances. The hard workouts (25x400, 12x800, 5x1600) were actually the lower mileage days. The longer runs (3x45 minutes) and segments/fartlek all just depended on the pace your group ran. Pre-race easy days (3x45) were about 17 miles and segments on Saturdays probably added up to nearly 20 miles but that was just for group 1. We ran these runs over set loops and we'd just count up our loops to figure out how far we ran. Mileage would also come from 60-90 minute "on your own" Sunday runs and I suspect that most people below groups 1 or 2 probably skipped those.
Suffice it to say that while workouts were hard, mileage was based on what you could handle and what you were willing to invest. Most kids near the top got that way because they also ran in the summers where there always a number of kids that put in 1000+ miles for the summer. The most extreme mileage and workouts came during "Camp Olympia" week which was 10 days where we averaged 25 miles / day. So running this kind of mileage during the season really only was done by those who put in the work to make themselves durable enough to handle it.
We did have a few people in the "hospital corp" that would spend the workouts walking a lap and doing "30,30,30" (push ups, sit-ups, jumping jacks). One of my brothers spent a fair amount of time doing this but he had some leg structure issues that made running harder for him. But I recall fewer people injured at York than my son's high school team where they don't do a lot of mileage, enough warm-up and cool-down and weight training. I find that more kids get injured constantly competing really hard without enough durability that comes from mileage.
Sorry for the long post but I loved my time at York and though I was involved in a lot of things (APs, orchestra, math team, latin club, worked, had a girlfriend) I would say that Mr. Newton, the lessons he taught us, the team, my running workouts and races, experiences (including running with Seb Coe when he came to our workouts and even drive him to Doc Durkin in Mr. Newton's Camaro) were the things I remember most fondly from my high school years.