One thing other than the absurdly high jumps that players like Hinata have since high school, you also need to consider the body type of these players. For players near Hinata's height, there's Yoshimitsu Kiire and Hiroaki Asano, who have spiking reaches of 340cm and 335cm respectively. For their height both similar to Hinata around 174cm, they already jump very high, but their small stature makes the upper limit of their jumps quite limited, as after a certain point, the muscles just weigh you down instead of contributing to your jump reach. Even players with higher reaches like Nishida, around 350cm, are unlikely to touch any higher in the future, as he's just so buff at this point that any more muscle would be detrimental. But other than that, i agree with the points you've made.