Facebook will drive something like 10-50% of people to add their store if it's the only way they can have their insta/whatsapp/fb/whateverthehellelse.
Google will probably roll out a play store as well. I don't think they're going to be as overtly evil, but they're still going to be be going around Apple's privacy protections if at all possible. (Why not? I get the feeling that FB is more on the back foot with metaverse and other flat/failing metrics, and google has more to drive people to them between Chrome, Android, and GApps.)
And others? There will probably be at least 10-100 app stores, and I would be shocked if there wasn't one that attempted to do things like a hidden RAT/Rootkit. I'm not saying that the app store review process solves a malware problem, but it is one layer in a defense in depth. It certainly has kept my extended family's devices in better shape than their computers, which I've had to clean occasionally.
This is a version of good of the many vs good of the few (Sorry, been looking at Star Trek lately). On the one hand, there are companies that would like a bigger hit of the pie, + a fringe of people who have enough knowledge and skills to manage to manually setup a secure phone with alternative/os/apps. On the other, there's Apple and a vast swath of humanity where the iPhone/iPad is probably the most secure computing device they can hope to own, and is yet still useful.
I dunno. Maybe Apple could allow stores on their phones, but still take a % of any purchases, to annoy EPIC and their ilk into buggering off.