That's exactly it, so many users are afraid that this will mean every random app you download will have a credit card entry field. Nope. Those random apps will still benefit from the simplicity of the system IAP, one tap, auth, done. The ones asking for a credit card will drop in ratings and search results.
The big players are the ones that will switch, amazon, Netflix, Spotify, Hulu, etc. And beyond that, competitors like Square and Stripe will release SDKs that make purchasing just as easy as the system IAP, and will actually force Apple to improve their system.
If Apple thinks hosting costs are of any consequence, then charge people for hosting if they don't actively use IAP. For 99% of apps hosting is pennies on the dollar, but for games like Fortnite it may actually cost a decent amount, especially for the binary size.
The end point is that there are no technical limitations to anything here, it is all political and Apple has the ability to change this at any time. There just isn't any point when they can continue to rake in 30% of every digital subscription service on the internet that wants to exist on their platform.