> this 30% is more or less a lock-in cost for the only official way to do business on IOS
As an app developer you're pretty much "screwed" TBH. You don't have a choice as to what platform your users choose (as long as you want to be in the market). Let's say Apple allows sideloading, but it is somewhat tedious and most users choose to stick to the official App Store -- then you're back to where you were, because you still want to sell your app/services to the users who stick to the official app store, and presumably your app is not so essential that users will actively switch if you dropped support for the official App Store.
If as an app developer you could influence the platform your users choose, then you would have asked them to move to Android and directly download your APK already, instead of bickering with the App Store (or even Google play store). The fact that you aren't proves that you're still at mercy to your users decisions, and whether they decide installing your app via sideloading is worth the trouble.
I'm not trying to denigrate you, but I suspect you might have unrealistically rosy expectations of the world where Apple is forced to allow sideloading.
