1. Not everyone likes skiing the same way.
a. This means not everyone will enjoy staying on a green trail until they learn perfect parallel turns. They'd rather quit skiing than do this.
b. The challenge of getting down difficult slopes is the only thing that brings them up to the mountain, and they don't care how they look.
2. Wedge skiing is extremely effective, especially for little kids.
a. You may associate beginner terrain with wedge turns, but that's typically because instructors move people towards different styles early.
b. If you don't push a little kid to parallel ski, they can quickly develop skill to wedge all over the mountain at virtually any speed, terrain, and steepness in bounds that typical skiers with parallel turns will exhibit. Wedge skiing does not mean that a kid can't competently and safely kick butt on double black and have a blast doing it.
c. It seems that wedge skiing becomes less effective as skiers get bigger. Probably the nonlinear relationship between surface area and volume causes greater physical exertion for wedge skiing with larger bodies.
In conclusion, the best strategy for developing the best skier is too boring for many people. Those that love skiing are happy with that path, but those with different interest would rather just do another activity. Is there a mandate that only people with intense passion for skiing are allowed on the mountain? Certainly not, and what you discover is that when you let people find joy skiing their way, they end up having a good time and are happy to come back. You won't find them on the mountain for nearly as many days as us, but you will find them up there a lot more than if you force them to ski greens until they meet your satisfaction. I understand that some people get ingrained habits from wedging and stemming that they can't break, but there are also others that can transition from wedge skiing very naturally. They do eventually find that joy we have and end up skiing well, whereas they would have quit if the black diamond challenge wasn't allowed to be their motivation; i.e. if instead form or a particular style were dictated to be their accomplishment. So, the moral of the story is that there's nothing wrong with the approach in the video for some people. It's what floats their boat. Different strokes for different folks.