Yes, the depth jump should be quick but the general consensus for 2-leg jumpers is that that comes second to the height attained. So the height you get on them should be the primary concern, and the quickness of the jump should come into a close 2nd place.
But considering what you're describing, you sound like you got more and more and more quad dominant as time went by. That's not necessarily bad news (a lot of the great dunkers are kind of quad dominant, even Derrick Rose was very quad dominant) but it's not good news either.
A different approach for you to consider is to do a lot of hip dominant movements. If you choose to squat, go for a low bar squat. Also do posterior chain assistance work where the emphasis is on the hip extension part of the deal. Think glute-hams, hip thrusts, reverse hypers etc. If you have enough money, buy a kettlebell (say, a 24 kg one) and do KB swings daily in your home. Make sure they are hip dominant, basically a hip hinge swing, not a squat swing (or else you're defeating the purpose of the exercise itself).
In terms of plyometric work, I would go with hip dominant plyos. What are these? They are bounds. It doesn't have to be 1-leg bounds. For you as a two leg jumper, you could go with 2-leg bounds for length. Just do these. They are more hip dominant than depth jumps (which are quad+calf dominant) and will teach you over time to use the hips better.
After you get good at 2-leg bounds for length, you can alternate in between 2-leg bounds for length and 2-leg bounds for height. The hip potentiation you get from doing the bounds for length will carry over a bit in the 2-leg bounds for height.
Check this post out by Lance:
http://www.adarq.org/lancests-performance-blog/some-jump-plyo-explosive-strength-workouts/So, if I were to personally train you, my program for you would be this:
2 strength days, 2 plyo days
Monday: Strength 1Low bar squat: 3x5 (use a weight that makes the last rep of the last set difficult. the other reps should be medium-difficulty (definitely not slow grinders) - increase weight when the last rep of the last set is still pretty fast);
Hip thrust: 3x10 (use the same weight rules as for the squat);
Calf raises: 3x12 (same weight rules);
Tuesday: Plyo 1Dynamic warm-up
50m accelerations x 3 (gradually build up speed in a relaxed manner, don't go all-out)
(Double leg bounds for length + Double leg bounds for quickness) x 3 x 20m - Do one set of bounds for length, then do a set of bounds for quickness (where the length is not that important, but the ground contact time is - so shorter bounds, but less time spent on the ground). Repeat this cluster 3 times. Rest as long as you need in between sets.
Donkey ankle bounces: 3x15
Stretch
Wednesday: Active rest - go play some ball, do some easy running, even try some jumps if you're fresh enough, BUT DON'T GET FATIGUED. Remember, it's REST day. So go and play around a bit but at the first sign (or even before) fatigue, go home and stretch and recover.
Thrusday: Strength 2Deadlift: 3x5 (work up to a heavy set of
leg-driven deadlifts (don't use your back to lift it, it won't help your athleticism) and then take 10 kg or so off the bar and do 2 more sets of 5);
Natural glute-ham raise: 3x6 (put a lot of padding under your knees (aerobic mats, spounges etc) and use as much assistance with the arms as needed);
Calf raises: 3x10 (use a heavier weight than on Monday, advance when the last rep of the last set is still fast, DON'T BOUNCE by the way - do them completely under control, slow eccentric, fast concentric, pause at the top and bottom);
Stretch
Friday: Plyo 2Same as Plyo 1, except you measure your 2-leg bounds instead of doing them for 20 meters - you do 6 2-leg bounds for length (per set) and put a cone on the ground, and measure the distance. Note that distance and the next time you do Plyo 2 the next week measure the distance again and put that cone back there at your measured PR. Try to beat that PR as you advance through this program.
So you will do:
Dynamic warm-up
50m accelerations x 3;
(6 2-leg bounds for length + 20m 2-leg bounds for quickness) x 3;
Donkey ankle bounces: 3x15
Stretch
That's all.
If you do this, which is a much more hip dominant workout than what you've done over the years, you should see some improvements. You just gotta keep at it and believing in it. It also has a low enough volume (vs what you've been doing lately) to allow you to actually adapt to the stimulus instead of getting injured. In terms of stretching,
stretch the quads and hip flexors daily, preferably a few times per day if you can. This will allow you, over time, to engage the hips better.
But if I see you say in 3 days that you're doing something else (assuming you agree to do what I layed out here in the first place) - then all my time spent to write this has been in vain.
Finally, every 4th week cut the strength work to 1 set instead of 3 for the squat and the deadlift, and for the plyo days go and try to dunk. I don't care what. Tennis balls, whatever. See if you made progress in your jumps.
As time goes by doing this program, you're going to get more specific and try to dunk more often (hopefully with a more hip-driven jump) while decreasing the amount of plyometric work (bounds).
