Hypothetically, without apple doing this, opening a PWA1 app can caused its data to be siphoned off by PWA2, up to isolation of the browser.
Whether or not that is a legitimate enough concern is up to each individual.
If it all boils down to "Apple users expect Apple to have control over everything, and if that expectation is violated, it will be really bad", then I'm sure EU regulators will handle it. Is there anything I'm missing from a security perspective?
If a browser can add PWA, they can claim they’re installing an app, and it would not be clear to a user that they have a web app, not an isolated app.
Now, none of these pseudo apps are guaranteed to be sandboxed from each other but the user cannot differentiate between apps that do provide security.
One webpage accessing the resources and data of another webpage is among the most basic of things globally known to be disallowed. This sandboxing reasoning is extremely bad faith.
Their behavior is akin to a small, bratty toddler throwing a little tantrum, but instead of being a small toddler, it is one of the largest corporations on the planet. Their "little tantrum" impacts lives and livelihoods, because they are upset a population has reps that actually represent them.
I hope they get what they deserve.
Except they are! Any browser worth their salt have been doing isolation since the dawn of time.
Or do you really think bing.com can manipulate google.com cookies and storage?
Yes, a good browser does. But you’re still leaving it up to each individual implementation, and the DMA rules that Apple cannot judge accordingly.