And to add to that - what you're doing in the weightroom does not really promote hip extension and DOESN'T promote hip hyperextension AT ALL. And these two things are paramount to jumping and being athletic (and even healthy).
Could you do stuff for the actual hip extension and hyperextension in the gym? Well, yeah, you could do hip thrusts, you could do KB swings, you could do cleans and snatches.
But you could also do hip dominant plyo work (bounding, off both one and two legs) and jumping and sprinting in general. These also promote actual triple extension instead of the deceleration that occurs with squatting at the top.
So, the thing with the squat is yes, it's the best muscle builder exercise. But it's not THAT specific to jumping. It's an assistance exercise to jumping, running, sprinting etc. These are all displays of reactivity.
You don't get athletes going to a spot, taking 10 seconds to pause and take a standing vertical jump in a real life, based 100% on their squat strength. If you were training like Kingfish specifically for the standing VJ (although I don't know why, but still) - then yeah, squatting alone would kinda make sense.
But if you want to be an athlete, if you want to be able to USE all that strength in a "functional" manner - that is - jump and dunk in games, get past your defender, be able to change directions etc etc etc - then you gotta do reactive work. It's not that complicated to understand.