It
is Econ 101, and of course all this is theory - but that's the idea right, we are describing
why it is in Apple's interest to do what they are doing. You are prescribing a change that goes against basic economic theory and also isn't the behaviour being observed, so I personally don't think that criticism is fair!
The main thing your comments miss is how apple is going to make up for the immediate shortfall in profit from your proposed changes. Bear in mind, they need to increase revenue 5 times to make the same amount of profit.
It's fine to hand-wave about how Apple should provide volume discounts because everyone else does, but you don't really provide a reason for why they should do that from a financial perspective and how they can do it without loosing a majority of their profit (everything is a soft-benefit which doesn't account for the huge financial losses this would incur).
I don't mean a bullet point, I mean like "I think a reduction of the fees to 10% would translate to a 20% reduction in the price of apps, and that would encourage people to buy 5 times more apps".
Or that all the money these big companies make will be so inspirational that 5x new developers will enter the market and these will, on average, be just as successful as the previous developers with zero cannibalisation.