Go ahead, I'll wait.
There are plenty of Linux distributions that use immutable root volumes. They protect the user in a huge number of ways by preventing the system from getting hosed (either by accident or by malicious unauthorized users / malware). Apple made the decision to do this for their users, and it has prevented a HUGE amount of tech support calls, as well as led to millions of happy users with trouble-free computers.
It also hasn't stopped users from installing Chrome and/or Firefox on their Macs, and millions of ordinary users have.
You seem to be ignoring the part where you can't install the Chome and/or Firefox browser engines on iOS and the apps with those names on that platform are just skins over Safari. Notice in particular that the iOS version of "Firefox" can't support extensions.
But hey, maybe some weird shit happened during the clone years that I’m not privy to.
Just an example… and yes, I know the EU ruling but it’s still fitting.
Compare the games console market. Nintendo is allowed to say you have to go through them to sell games for the Switch, ditto Microsoft with the Xbox. Sony doing the same thing with the Playstation is exactly equivalent, but they're approaching the sort of market dominance where it might soon be illegal for them (and them alone) to do that in some markets.
Copyright (e.g. over iOS) and patent (e.g. over iPhone hardware) are explicitly government-granted monopolies. Having that monopoly is allowed on purpose, but that isn't the same as it not existing, and having a government-granted monopoly and leveraging into another market are two quite distinct things.
> Compare the games console market.
Okay, all of the consoles that require you to sell you to sell through their stores shouldn't be able to do that either.
> but they're approaching the sort of market dominance where it might soon be illegal for them (and them alone) to do that in some markets.
Wait, your theory is that a console with ~50% market share has market dominance but Apple with ~60% of US phones doesn't?
The monopoly that Microsoft held was the home computer operating system market, first through DOS, then later through Windows. Holding a monopoly like that isn't illegal unto itself. What they were actually found guilty of was unfairly leveraging their monopoly on the OS market to gain the upper hand in a different market (the browser market). The subsequent range of issues we had with IE6 (compatibility, security, etc) was a result of Microsoft succeeding in achieving a monopoly on the browser market through illicit means.
Likewise, "Apple has a monopoly on the App Store" is just the same amount of nonsense. What you could argue is that Apple has a monopoly on the home computer market, or the mobile phone market, and that the way they integrate the App Store should be considered illegal leveraging of that monopoly, but that argument simply doesn't hold water — Microsoft's monopoly on the OS market at the time was pretty much incontrovertible, you simply couldn't walk into a shop and buy a computer running something else (except maybe a Mac at a more specialised place). Today, just about any shop you walk into that sells computers will probably have devices for sale running three different OSes (macOS, Windows, ChromeOS). Any phone place will have iPhones and Android devices, and probably a few more niche options. Actual market share percentage is nowhere near the high 90s that Microsoft saw in its heyday. At most, Apple is the biggest individual competitor in the market, but I don't think it hold an outright majority in any specific product class.
Mind you, I think that there is a good argument to be made that the Apple/Google duopoly on mobile devices does deserve scrutiny, but that's a very different kettle of fish.