I fully agree, imagine if MS had made Windows apps on W10 only come from their store. Anybody saying that the solution is "just buy a mac 4head"*, like they love to do with mobile phones, would be laughed out of existence.
*: It's great to have options, and linux should be in here too, but that would be like telling a normal user in this situation (mobile market) to go buy a Pine phone, which for very few would work the way they expect/need it to.
If most people actually choose iOS/iPhones primarily because of the App Store quality/protections/ecosystem then people will continue to choose the App Store regardless if sideloading is possible - after all we just said that's the whole reason most bought the phone in the first place. If on the other hand people are choosing iOS/iPhones for other reasons and you're worried nobody else will use the App Store anymore then I don't really buy "there aren't enough of us so it should be allowed to hold a captive market to support our use case" as a reasonable argument even though I see it quite often on HN.
Why? Android is a legitimate alternative, one that the majority of the world population uses. You have many makes and models of handsets from which to choose. You want the polished apps with a completely open and free environment. Maybe you should ponder why such apps don't exist for the open and free ecosystems?
and the argument about "giving developers power" simply doesn't hold any water. android openly allows sideloading with the google play store having very similar rules to the app store, and yet i can count the number of major apps that force or even offer a sideloaded version on one hand. the only ones that come to mind are fortnite (removed from google play) and telegram (on play store, but sideloaded version has faster updates and less censorship).