It always amazes me in these debates that so many high school coaches come up with unlimited excuses and reasons why kids won't run, can't run that many miles, parents nix their plans, administrators, other sports and coaches dictate how their programs can realistically be implemented.
Kids play soccer, baseball, basketball, and participate in swimming, ice skating, and gymnastics year-round from the age of 5, but high school runners can't run if it interferes with their other extra-curricular activities, and their parents aren't your best buds, 100% behind your plan.
Whether the OP's plan is too much for the average high school kid may be more of a reflection on who makes up your teams, rather than what can make a young runner more successful. Do coaches from the sports above keep every straggler who shows up on the team and bend over backwards for them and their parents when they say they can't or won't follow their programs?
It sounds as though as many as 50% of coaches who respond to these type of threads treat high school cross country and track as recreational activities, citing participation and other various factors as the primary goals of the program, bending over backwards to keep everyone involved, no matter how the kid or parent feels they need to actually comply with the coach's rules, plans, decisions, etc. It's like listening to a bunch of people-pleasers who don't want to offend anyone, or step on any toes, while they are supposedly in charge of their own program. When you mention the word "development," these coaces jump on it like some evil Eastern European concept that can't work in the US.
These same coaches cite their own and their runners' success at the local, conference, and state level, and seem to believe that means they are fulfilling their duty, let the chips fall where they may beyond that. Meanwhile, we have all these kids in the US "participating" and competing at this supposed high level of success coaches have defined in high school, and why is it 20, 30, 40 plus years before guys like Webb, Rupp and Fernandez break American high school distance records?
Bottom line, the kids have between 4 (and maybe, hopefully) 8 years of serious training and competition, then they get a real job, sit behind a desk all day, get married, have kids, and wonder what could have been. Why not do your utmost, given your position, to maximize their potential when the opportunity exists, instead of contributing to their fears and doubts by coming up with excuses and reasons for not fulfilling a most valuable lesson: striving for excellence in any endeavor you undertake, especially one which you voluntarily choose to do? After all, no one is twisting their arms to join the team.