Not saying that the trade isn't worth it, just that, well, now that Pandora's box is open, it's coming to get you, even if you don't want it to.
1. Apple won't stay competitive for its major partners in the app store.
2. The app will be really important for you with no alternatives.
3. It will be both important and won't be up to your standards established by Apple.
My suspicion is that if it provides really interesting functionality, it will have enough competition that you will be able to choose from.
The major danger comes from scams targeting uneducated users, however, if Apple really wants to protect them, it will make everything possible to maintain their app store as a viable distribution channel.
I'm thinking of scenarios where you don't specifically want the app, nor does it offer any particularly interesting functionality - it's just a platform lock-in effect.
As a trivial instance, you can't install Fortnite on Windows machines without going through the Epic Store. Yet, the value of Fortnite isn't how the game plays, but the skins & community - things that cannot be replicated by another app.
This is something iPhone uses use all the time and this did not happen on Android.
Some people just like golden handcufs.