This video explains in detail, but in a way anyone can understand. How the myth that "amplitude is everything" came about. A simple wrong conclusion that was jumped to by a group of academics years ago because they did not look at the bigger engineering picture.
Note: This myth has been disproved now not only in theory, but also on the floor of studios where level force 2 -- > level force 5 machines operate side by side, running at exactly the same frequency and amplitude. But giving completely different perceived exertion level workouts.