Those airlines you have quoted don't require enough supply to keep even a fraction of the current training supply in your prefered method viable.
So although they wouldn't completely disappear they would be a fraction of the current over supply. And if there is another slump due to fuel price or some other global hit to aviation and those airlines stop the cadet schemes the future is grim for that part of the training industry.
Of course if the supply dropped to the current level of demand then there would be no capacity to ramp up production when they required more than the current.
We have no arguments about the cadet schemes if they can get on one go for it.
Its the self financing of the same training which needs to be highlighted as a poor investment of both time and money.