Lots of questions. I’ll do my best.
CNS tolerance is not a function of genetics, but more so of development and time. Your ability to tolerate high outputs will develop over time as you build a base of high-intensity work beneath you. However, you are also building a base of low intensity work that will help you to recover more readily from high output workouts/races (assuming you are following an appropriate training program and progression). This is why Charlie liked the short-to-long approach, which included high-intensity runs throughout the year (building a large base of speed work). His contention was that a long-to-short program included a lower overall volume of speed work (and less exposure to speed throughout the year) and, thus, made the athlete more susceptible to injury and CNS overload in the latter stages of training.
This all makes sense in the case of Powell. If he is following a long-to-short program, it will take him longer to reach his peak (i.e. he needs a min of 16 races to be in top form), but it will also make him more susceptible to injury when he is in the thick of competition season with lots of high intensity races week to week. We could say that his CNS tolerance is low due to the progression of training he is following and the lower exposure to speed work throughout the year.
Of course, it is a double-edged sword and when you get to the latter stages of your career, you must back off on the frequency of high intensity workouts because you cannot tolerate higher volumes of work in the high-intensity zone. This could be both a central and peripheral recovery issue, as testosterone levels will begin to level off and drop as athletes enter their thirties. This is represented in one of the graphs we created for Charlie where training volume at the high-intensity level drops off after a number of years. (See below - lower diagram)
Developing athletes with less strength may very well improve more readily on a long-to-short program because of their reduced power output. And, they do need to develop a base of general fitness and strength. They may have lower CNS tolerance, but it doesn’t matter because they can’t training at a high enough output to create that level of fatigue. Remember, much of Ben’s initial training was long-to-short in structure.