I'll offer you my opinion, same big bucks as the others!
You seem like the type who respects things when they are not sugar-coated... so in respect of you, I have tried to present my opinions(answers) to your questions unsweetened.
A beginner has the same option as you to pay 90$ for a one hour private lesson to learn to ski and choose or require a L3 cert PSIA instructor. In this case, they are paying the same amount and getting the same qualified trainer as say you, an accomplished skier, who skis 20-30 days a year.
However, not many never-ever's do this... why? I suggest to you because they know they do not need that level of qualification to just learn the basics of how to use the gear, how to turn and how to stop in order to get around on the easiest of green terrain on their first day or weekend of skiing. As a result of all this, I know my hill offers EZ-Ski 1-2-3 packages that cover three days of skiing (Tix, Group Lessons and Rental Gear) for $109. When you pull out the cost of the lift tix, the rentals, then you reach a cost of instruction that is in the vicinity of 1/10 of the 90$ you are paying to have the superbly qualified instructor of your choice for 1 on 1 training.
I further suggest that while you are entitled to have your own opinions on how things should work, the way things do work is the never-ever's, >99% of the time, end up with qualified instructors.
The requirements you posted are the bare minimums to just come and try-out for an instructor job. Not all of those folks make the cut. The folks who do make the cut do usually recieve a lot of training on how to teach the hill's preferred progressions and as the years tic by the instructors gain further experience and skill and gain opportunities to teach to higher skilled skiers.
Bottom Line, in the states, if you are willing to pay $90/hour(or whatever the hourly private rate is) as a never-ever then you, too, can make an appointment with the very finest professional instructor at your ski area for an hour teach you to ski.
The Ski Schools are in business to service a need, they are a business and all business is about extracting dollars from willing customers in exchange for value. There are 9 levels of client skiing according to PSIA dogma serviced by PSIA and most US ski areas. At Whitepass, Instructors must be at least 2 levels above the groups lesson level on skiing ability they will be teaching as discerned by the ski school staff to the criteria defined by PSIA for those 9 levels. Needless to say we do not see many level 8/9 group lesson requests, by that time those are usually private lessons or other form of coaching.