I think people overlook the height factor involved in the SLJ which could help explain why throwers (aside from there strength/power) have large SLJ. Taller athletes are at an advantage in in SLJ
Furthermore, although it is not correct to say that an athlete needs ‘x’ distance in the SLJ or VJ in order to run a 40 in 4.4, I do believe younger athletes will most likely see an increase in speed when SLJ or VJ is improved, whereas the higher level athlete might not.