You are both right, achieving a windmill is a function of both things:
-If you improve the speed you do the windmill motion, you will end the motion at a better position, so you can dunk it ( if it takes too long you will be on the way down ).
-If you improve your jump(hangtime) you do the same thing, you can take a little more time to do the windmill motion and still be at a dunkable height when you finish it.
-If you make your reach higher or the rim lower, you lessen the vert you need to dunk, so again you have better chances of dunking it on your way down.
Of course those do not apply to the extreme ends. So if your vert is 10'' and you try to windmill 8', you won't, because there is no time for you to complete the windmill motion. But for 'normal' jumps ( 30'' and above ) , 10'' of reach, or 10'' of lower rim, or 0.25 seconds of faster windmill motion can make the difference between dunking it or not.
2 October 2015
7 Days Vertical Jump Cure routine
Foam roll : IT bands, quads, hamstrings, glutes.
Stretch : groin, quads, hamstrings, hip flexors, calves.
Looks like quads are fine now. Looks like hamstrings/hip flexors tightness and abs strength are the weak links.