Not at all trying to defend Apple's behavior here, but that statement is not true. There are many indie devs making a living from apps. Margins in indie apps are usually very high, as in most cases the expenses are fixed - just your own salary.
It sounds like you are hiding costs of overhead. What about rent for your workplace (whether it is your home, a coffeehouse, or WeWork) and your utilities, especially electric power and Internet access, and your HW/SW tools, including your notebook, monitors, accessories.
Don’t hide your externalities naïvely like an Uber driver.
Say you need 100k profit after Apple's cut.
Scenario A: Apple takes a third of the App Store revenue. You need to sell in-app purchases for 150k. Scenario B: Apple takes no cut. You need to sell in-app purchases for 100k.
So the claim is, scenario B would be the dream, but scenario A is "nearly impossible"? What is fundamentally different between 100k and 150k revenue, if your expenses are fixed? This doesn't make any sense.
The comparison to Uber doesn't make any sense either, their costs aren't fixed. If they want to double their income, they must double their work.
Consider it similar to supermarkets or amazon. anticompetitive market practices and other dynamics make it so they are dominant. Now it's almost unfeasible to not sell your product in these places. They can now dictate you can not sell your product cheaper in your own store if you sell in theirs or the like. At any given time they might notice your success and decide to compete with you kick you to the curb with all advantages they can be expected to use.