Antitrust is not about whether people have the arbitrary ability to go around it, it's about whether people actually go around it, and if not, is that because one player entrenched themselves in the market that they are able to distort it.

I guess it depends. If Apple made iOS available on other hardware this conversation would be different, I bet. The problem with Apple's practices is the "ecosystem" approach. You get one of their devices and you HAVE to use their OS, you HAVE to use their core app bundle, you HAVE to use their store. And in a number of things where you don't have to, you're heavily incentivized or the competition is made less competitive. And now you're on a software platform that only works with Apple hardware, so now you have an incentive to migrate your other computing devices (laptops, desktops, smart TVs) to be from Apple, too, because that's where your compatible software lives.

It's the sort of practice antitrust laws exist to prevent.

Google is no saint and will do as much of this as they're allowed, but at least the nature of their OS and the diversity of manufacturers and OS customizations means they don't control the ecosystem end to end. The biggest manufacturer is Samsung, and they will ship with their browser, an alternate store, a different mail client and a bunch of OS modifications Google doesn't control, so Samsung and Google give each other some plausible deniability within the Android ecosystem oligopoly.