i've coached collegiately for several decades and have coached national champions and several top 10 teams in XC. I have a sibling who ran at the NXN championship. I've presented at several coaching conferences. I am not "out of it". On the scoreboard my record would be considered solid. This being said I don't go about things by saying "just gonna do an easy 3 and get outta here today". I would argue that I have experience and perspective on my side. It is from these things that I form my opinion.
You are correct that things like the event can be improved upon. Getting a new course for NXN is probably a good thing but it wasn't because people were whining about fairness. Likely the selection of a better course was to make the event better for all, especially the athletes. The new course wasn't selected to make things "fairer" but rather just "better".
I have mentioned that I wouldn't want 7/8 graders competing at the varsity level of high school sports. However, some places allow this and thus their teams are formed and compete as such. Those teams get the opportunity to compete for state championships per their rules and some win championships with these young runners. It seems to me that Nike came up with an idea that basically says - we have champion teams from all the states, let's see which of those teams is really the best. Nike then created an event NXR/NXN to determine this. Basically a chance for each championship team to compete against each other and now we have this great event.
Nike is not an association like the NCAA or any high school federation. They just created a really cool event for kids to showcase how their high school team (and some individuals) match up after their regular season is over. The opportunity to participate and perform at NXN is incredible. It is a lifelong memory and experience no matter who wins. Whether you win or lose at NXN isn't as important to me as watching the kids work hard, set goals, compete the best they can. What i've learned over my many years including as a coach is that life isn't always fair. I've also learned that any recommendations for improvement should be with the best interests of all in mind, not just those that work best for me. I don't see how things are improved if you exclude 7/8 graders from NXN. All it might do is reshuffle the deck a bit but the important stuff that I explained earlier (lifetime experience, goal setting, competing...) don't change at all.