I think this is the heart of the disagreement between people who like the iPhone walled garden (I’m one of them) and people who agree with you. I think it’s where reasonable people can disagree (except of course when it comes to broad legislation protecting or prohibiting such walled gardens).
I don’t think the iPhone is comparable to a personal computer like a Mac, even though of course the hardware and software architecture is very similar (and increasingly so). I still think that smartphones are, for most people (especially people who are aware of the key differences between iOS and Android and still make an informed choice to use iOS), much more like “integrated consumer electronics devices” like gaming consoles, or car infotainment systems, or heck even a microwave (your microwave probably also contains at least one Turing-complete stored-program architecture computer).