If Facebook is chomping at the bit to do this on iOS as soon as they can, then why haven't they done it on Android where they already can?
Nobody who doesn't opt in for privacy shredding will have their privacy shredded.
If you don't opt-in to privacy shredding then you will be locked out of being able to use facebook, whatsapp, and other "network effect" things that you more or less don't have a choice about without cutting out communication with large parts of your social network, so this is not really a "free choice" at all.
Right now those companies don't have the leverage to lock out Apple users. This immediately gives them that leverage and they will use it, just like they already have tried (and gotten their hands slapped for).
App store review is the only thing standing between you and Facebook demanding full permissions for everything, and allowing third-party app stores or sideloading is a mortal blow to app store review.
I understand that you don't personally care but the Apple customer base does, a large number of them specifically choose that because Apple is using their leverage in favor of the customer here. You can get the experience you desire on the dominant smartphone platform (with 85% of the global smartphone marketshare), just leave us the freedom to choose this experience as well. You're arguing that we should be explicitly denied this because it's not convenient for Facebook.
We don't need to sacrifice general purpose computing and user freedom on any platform so you can protect your false impression that your privacy is protected while actually giving it away cheap.
I believe Zuckerberg said it wwll years back when he called people who trusted him suckers.
https://arstechnica.com/gadgets/2019/01/facebook-and-google-...
that is the true red-line from a user perspective. go on and have your spat about whether 30% is fair or not, but the app-review process is the keystone on which the permissions system rests, allowing sideloading is tantamount to allowing all major apps full-permissions overnight and essentially making the permissions system meaningless.
the only viable solution I can see that allows third-party app stores would be to require that Apple still review all apps on third-party app stores to enforce the requirements surrounding permissioning (i.e. having a valid reason to request the permissions you're requesting) and they would still need to charge for that.
"third party app stores without any review, but Apple still gets a cut" would be the worst of all possible outcomes.