>You'll simply pick Safari, never sideload an app, and pay with Apple Pay. We can coexist.
This isn't even slightly realistic.
It's a mistake to believe that these changes won't have run on consequences for developers. This isn't an outcome where you can have your cake and eat it too. It's not like everything will stay the same, except now developers have a bunch of extra freedoms. That exhibits no ability to think even one-step ahead of what these changes will bring about.
We already know two dominating outcomes of these changes: 1. the path of least resistance for companies/developers (driven by cost), 2. Evasion of unpopular app store rules that solely exist to protect consumers from nefarious predatory apps (driven by profit).
For example (1) your idea of a user being able to have control over their device is naive. Users won't have a reasonable choice to not side-load/use a 3rd party app store when the app is required by their employer, or insurance company, or bank, or medical/insurance provider, or state services. These will come about naturally because it's the easy way of getting around app store procedures, quality control, limitations. I.E. It'll cost less to produce these apps, so they will come out naturally from economic factors even before simplicity/laziness/frustration with app store operators are considered.
For example (2), We already see how technology is being abused to closely monitor employees, customers and students to the point of unreasonableness. These will now extend into ones phone, when previously such apps weren't possible due to being forbidden by the various app stores. Imagine insurance companies requiring the user to have an app installed so they can negate your insurance on an AI-driven whim: if it detects a medical condition (such as visiting an abortion or sexual health clinic, or the detection of AF through the accelerometers), or if the user drives too fast, or visits dangerous areas/countries, or conducts any kind of risky activity that AI can accumulate from text messages, location history and on device sensors. The sky is the limit, and the idea that you'd just change insurance company is naive: they'll all do it, and they'll price their products so you don't actually have a choice.
However we don't even need to peer into the future to see what happens if the reins are taken off, we saw how app testing certificates were abused to trick users into installing privacy evading/tracking apps. It's so naive to pretend that this isn't going to happen now, especially if all it takes is a click on a website.
Side note:
We have these new changes, but we don't have the corresponding consumer protections, nor any realistic way of enforcing them even if we did. There is no equivalent authority to regulate apps. It's like the bad old days where anyone can make and sell a medication, we'll need the app-store equivalent to the European Medicines Agency.
And to think, people were worried about AirTags. Keep your phone close and trust no ones app suggestions, as now the phone can be effortlessly turned into a keylogger, an audio + visual listening bug, a live location tracker and any app can trivially scrape the phones contents: photos, contacts, credit cards the list of possibilities are endless, because by design smart phones were made to be carried around, contain more sensors and personal information and rely on protection bits provided by the various app store so apps wouldn't have trivial click-through access to protected silos of information. (Why do we know this will be a problem? Because it was already a problem.)
So now we get to see this all unfold, as if it wasn't completely predictable.