I didn't say anything about 2 high school athletes - the training theory is the same. If you don't train speed you will lose whatever natural speed you were born with. In fact, the younger you are, the GREATER THE NEGATIVE EFFECT of speed loss with high volume.
High volume without optimal form or strength is WAY WORSE than doing 1 speed session per week with poor form/strength.
High school sprinters do speed and they stay pretty healthy and they continue to improve in college and beyond.
As the other guy said - you don't really "lose" speed. Lots of mileage and aerobic training conditions your muscle fibers to work more aerobically, but you can get the speed back relatively quickly if you want to.
Magness is one of the biggest proponents of sprints - how did Allie Kieffer respond to that training? She is a 90%+ slow-twitch runner, broke down doing his sprints and left him for Hudson. She stated multiple times she hated the sprints that Magness gave her and never felt good doing them.
Of course the HS sprinters like sprinting and continue to improve - they are born with a lot of fast-twitch fibers, their bodies are made for sprinting. Put them on 100 mpw or even 40 mpw and ask them how they are doing, they will quit running immediately if they didn't get injured during that high mileage time, their bodies just aren't made for that type of training.
Would you train someone with 90%+ slow-twitch fibers, like Salazar with all-out sprints? Elite milers have great speed and do all-out sprints. It's necessary to have good basic speed to run a 47-48s 400m and to be able to close a mile in 50-51s. But on the HS level, you would be focusing on the wrong thing. First these kids need to get their mile times to 4:20, then 4:10 and then sub 4:00. Then there is enough time to think about introducing sprints to get that last 1-2%.
Drew Hunter, and Grant Fisher both were fine without sprint training - Drew only did strides, basic Tinman training and Fisher was not trained with speed since his coach believed that all that soccer training provided him with the speed he needed. Fisher was faster than Hunter from 100-400m, but it might have just been natural talent and not the sprinting from playing soccer while Hunter did mostly CV and threshold training.