I agree with your whole post, expect this part. Most people can work up to being able to do quality loaded jumps and depth jumps. And they offer a different training effect than regular jumps. Everybody who can do them efficiently will get something out of them that regular jumps wont give them. It's not just as stimulus scale (same type of stimulus increasing in intensity with every different movement) it's a different one altogether. It's like comparing a deadlift and a power clean...similar movement pattern, a lot of the same muscles involved, both are done with weights, one is fairly simply the other is more complex is done properly. But you can't say "if you get good at deadlifts you might never need the power clean", they develop different things.
Same with depth jumps and regular jumps.
I'm not saying to jump into (ha!) depth jumps to get the different stimulus. But that they certainly offer something more and different provided that you can do them right.
And saying that few people can do them right is exactly like saying that few people can do a snatch or clean & jerk. I've taught the Olympic lifts to people who most would have said have no business doing them and they all work up to a pretty good level of performance, it's all a matter of proper progression. If you start an athlete telling him "you need to be a great athlete to do depth jumps, so you wont do them or might not ever need to do them" what are you telling them? What are you doing to their mindset?
For example I train a young female (22) she was grossly out of shape. When she began to learn the Olympic lifts snatching the empty bar and cleaning 55lbs was HARD and ugly. 5 months later she is clean & jerking 190lbs and snatching 140lbs and she isn't a naturally gifted athlete either, but she trains hard every day and challenge herself, not accepting limitations or failure.
If you pre-program limitations in an individual mind you are doing a horrible job as a coach.
True some people might take a long time to work up to thehigher echelons of the progression model, but with proper work everybody can climb it up.