Good post. Very informative. I'm certainly not calling BS on what you wrote. I didn't realize there were that many non-Nike D1 programs, but 'that many' is still just a few. Don't they have the so-called P5 locked down? Maybe not: I'll admit I don't know exactly whom that includes. But the Pac12 plus BYU seems to cast a big shadow distance-running-wise in the States. Include a few others - OK State, U of Portland, New Mexico - soon you're covering the alma maters of nearly every American pro. Not all. NAU, as this thread is discussing, is a glaring exception.
Now about high school. As I wrote above, when I went it wasn't Nike-oriented at all. They were just picking up steam back then. But I've been noticing the 99-100% trend since the days of Running Times. The first photo that sticks in my mind was a starting line of a random high school track race. Waterfall start, so not a sprint.
'Random' is accurate here because no caption was given and it wasn't supposed to be a particular event. The column was about high school track in general. Maybe 'how to get people to come watch it' or something. Anyway, the photo was taken at ground level and you could only see below the knee. Every shoe clearly visible and easily indentifiable. All Nike. This may have been taken aroung 2010.
A year later or so was a multi-page spread about high school XC. A couple other brands worn by kids standing around (as opposed to in a race), so that gets me to the main point. I'm only judging by what kids race in. I don't really see footage of high school training with the exception of one video I saw of NP on YT. No student there would be caught dead with anything else, so even the training footage is Nike as far as that school goes. (And the subject of this thread just got out of there.) But with rare exceptions, I haven't really seen what teenagers train in.
Going by racing, however, it's been 99% Nike for quite a while. It's probably 100 now. The last exception I'm aware of was the kid who went sub-4 outside of Folsom, CA (Sacramento area). Though I don't, some of you will remember his name. He was in NB. The rest of the field, well, you know.... That was a few years ago now. More recently, threads here about sub-4 attempts and other high school exploits have pointed out that the entire field is Dragonfly-shod.
I'm sure you're right about the college thing. You very well may be about high school TRAINING. (Still 90% there and at NP it's 100 even for training.) But as far as high school RACING, they simply don't wear anything else that I can see.