They can help developers with ad discovery in a bunch of different and better ways that are less hostile for devs and users.
Thank you for the funny typo "ad discovery"
"We curate the finest ads for your consumer experience.."
Ad discovery is more Facebook and Google’s business.
The above has nothing to do with Apple's cut on other people's work. That is just exploitation and is unrelated to increasing the quality of the experience for users. On the contrary, it makes life harder for developers wanting to bet on quality and instead encourages shovleware and deception. And this is exactly the outcome one sees.
The app store experience is what is antithetical to Apple. There is nothing premium about it.
They do eventually use this power to force you to buy a new house. They use it to mark perfectly capable devices as obsolete e.g. why is a MPB i7/retina/ssd with discrete graphics now being marked as obsolete? Why is an iPad4 not allowed ad blocking with no chance to install an alternative open OS?