I would hope that this “best case outcome” also comes with regulations to keep other giants (mostly Google) from marketing and cross-promoting their way into dominance on iOS, creating monopolies in the process.
For instance, Google apps shouldn’t be able to drive Chrome installs by presenting a sheet offering to download Chrome every time I tap a link in them, as they do currently.
Chrome’s quality is what’s usually cited as being the primary driver behind its rise to its current position of most popular browser, but the reality is that Google’s intense marketing is at least as responsible. In-app prompts, prompts in Google search, and Chrome getting bundled in installers for every other Windows app were big contributors to its momentum.
Of course it becoming the default browser on the majority of Android devices and Google web apps underperforming in other browsers also played a role but that’s a bit of a different topic.
I have no doubt marketing played a role, but Chrome and Chromium-based browsers were the only ones with a multi-process architecture for over half a decade after Chrome's launch. That meant a bad web page couldn't crash the browser or block the UI, which used to happen frequently on other browsers.
Firefox eventually caught up, but had lost much of its userbase and mindshare by that point.
WebKit went multiprocess with the release of WebKit2 around 14 years ago, with the difference being that the multiprocess architecture is part of WebKit itself and thus easily reusable — just embed a WebView in your app and you have it. This contrasts to the Chromium implementation where multiprocess is handled by Chromium rather than Blink, meaning to get multiprocess you have to ship the whole of Chromium and can’t just embed Blink.
That said this really only relevant for Apple platforms and Linux/Android, unfortunately. WebKit for Windows is somewhat in a state of disrepair.
For instance, Google apps shouldn’t be able to drive Chrome installs by presenting a sheet offering to download Chrome every time I tap a link in them, as they do currently.