As an iOS and web user, it is my desire that Apple doesn't allow other browser engines because immediately Google and other web devs will start pushing webapps that only work with mobile Chrome and we'll all be forced to install a Chromium browser to use certain websites, it becomes default and users will think "Safari sucks now, a bunch of websites don't work with it," finally ending Google's last bit of real competition in the browser space: Safari with its terrifying 17% marketshare.
That's not even getting into the resources/battery life aspect.
As a web dev, I happen to love some of the tech advancements in Chromium, and as a nerd, I'd be thrilled to see it on iOS, just for the fun technical novelty of it all. But allowing it on iOS will downright kill WebKit, as web devs will just code for Chrome (as they already do). The floodgates will be opened.
As a user, I value battery life, smooth performance, and system integration (technically and visually). It's great to use an Apple browser on an Apple OS, just as it is nice to use Chrome on Android—everything fits together.
Gosh, I miss the pre-Blink days when WebKit was able to benefit from Chromium, but alas…
So to protect an artificially inflated browser engine you're willing to remove user choice and freedom to prevent a competitor from doing well? Microsoft was learned this was illegal many years ago. When the US government went after monopolies and didn't cosign them.
> It's hard to make the case this is possibly in the users' interest.
Not in the least.
If anyone who wants can make a complete browser for iOS, then, for instance, Meta could come out with their own Facebook™ Browser that does extra super duper tracking on them and everyone they interact with online.
Or Russia/China/Trump/Obama/whoever you hate most could make their own browser that inserts propaganda into websites, redirects you away from sites that are critical of them, etc.
Or straight-up criminals could make browsers that steal your credit card info.
And a) Apple would be put in the position of having to do comprehensive testing on all these browsers to make sure they did not do these things, even in unusual situations, and b) do you actually trust Apple's App Review system to catch it all? 'Cause I like Apple, and I sure as hell don't. Especially in cases like the latter, where they could create a dozen profiles and have each one submit a dozen slightly different versions of their compromised browser (eg, one that's Skibidi Toilet themed, one that's got scantily-clad women (just PG enough that Apple won't ban them for that) framing the pages, one each themed for the MCU movies...)
This is about securing the phone in Apple's interest against the desires of the user.