Rusty Guy, very nice post indeed. You have clearly observed mogul skiers with a sharp eye and come to many good conclusions.
Braking at the waist
You are right about this braking at the waist. I do it too and it is like you stated yourself correctly the outcome of insufficient flexion of the leggs. Happens usually when I get tired and my leggs dont work like they should. This is what happens to dachan as well in the video and could be a result of his insufficient ability to flex due to his injury.
Also your observations of the upper body is correct. Lean forward and straighted out your back like you are horsback riding. Keep you upper body calm and facing downhill all the time and do all the work with your leggs. Imagine you are a car and your leggs and feet are the weels, suspention and the shock absorvers. The ide here is to keep the CM as stationary as possible to ensure a smooth ride. But a key to keep your body facing down hill all the time and to keep the CM moving down in the fall line as smoothly as possible is that you have to make lots of really short turns and stay in the zipper line. If you move away from the fall line your CM will also move sideways and this will shift you from mogul technique to regular skiing technique. I personally dont straighten out my back like Im horsback riding, plant my poles only with a small wrist movement and use very short skipoles. And I dont stay in the zipper line although I could if I wanted. My approach is to hit the bumps straight on and in the other direction and use the impact to slow me down. Dachan is following his ski tips with his upper body since he is not skiing in the fall line.
Porfessional mogul skiers dont edge much. Good example is all time best mogul skier Janne Lahtela who said he never attends to his edges in any other way than to make them less sharp. He uses 3 pair of skis every season and he changes them only because they get so scrached on top that they look bad on TV. If you want to ski in the zipper line you have to be easy on the edges and skid a lot. Janne also stated that it is important to have your weight primarily on your outside ski although you have your skis close together.
Im not saying that you cannot ski bumps with skis wide apart. Offcourse you can. Can you ski a GS course with your skis close together? Offcourse you can. I mean I can anyway. But there is a good reason for you to have your skis wide apart on a GS course if you want to do it efficiently exatly for the same reasons you have to have them close together in moguls. This is what I find so nice about skiing, you have to adapt your techniqe to the terrain. My definition of good skiing is the ability to adapt to reinin conditions. Mogul skiing calls for close position.
So back to your question.... "tdk6 would it bother you if I said that I could ski dchan's line with very little flexsion and extension using minimal upper and lower body separation with no knee banging, nice and smooth, as long as I kept my feet apart?" No, it would not bother me. If you ski dchan's line there is no reason for you to bring your skis close together. If you took a more mogul skiing line you would benefit from a closer stance. You also very smartly used the word "minimal" because this is exactly what you should use, minimal flexion and extension required
This is all I require from any move or technique in skiing in general, as much or as little as required in order to execute intended manuever properly. In dchan's case there was barely any flexion existant in both videos.