I know strength is mostly neurological BUT there is a limit to neuro gains. The light powerlifters cannot lift as much as the heaviest. Most models establish that neuro gains last ~2 years. So what do you do after thoses 2-3 years, when you reach a 'plateau' ? You have to grow bigger. It's why I believe that HST in a sense is also SST for people aiming for maximum strength and not only a certain degre of strength for a specific bodyweight.