That iOS polish is largely a byproduct of the walled garden approach. Users are incentivised to spend within the ecosystem due to the safety, security and support provided by Apple.
This argument would only make sense if the vast majority of Android spend was outside the Play ecosystem, which it is not. The second part "The safety, security and support provided by Apple." sounds more like a general Apple press release than something related to app polish.
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.
