They do, at the app level. As a developer you can install whatever app you want on your own devices, even apps which would never be allowed in AppStore or TestFlight (although still not with all the entitlements Apple’s own apps can get.)
OS level, your point stands.
You utterly do not own those devices. Apple sells a house where they kept the keys to all the locks, but people think it's ok "because they'll keep me safe and unlock my doors when I need them to!".
Nevermind the risk is mostly a marketing boogeyman in the first place.
You... don't think you can install your own software on MacOS?
They're both perfectly fine general purpose machines - except apple holds the keys to the engine, and only hands them out when they approve of the use case.
I don’t love where that leaves us but it does make me wonder whether a better compromise would be something like regulation requiring third-party app installs but with some kind of business liability & registration requirement so e.g. Epic could set one up but fly by night scammers couldn’t easily set something up and spam AARP members.
They bought them because it was a new category of device (and extensive marketing from Apple - although I don't mean to discount the product with that statement - very solid phones, but also very excellent marketing). If anything - the early tech adopters moved to the iphone because it was more open than the existing phones at the time, which were definitely not general purpose computers. The iphone got us halfway there - I'd like to see us take the last few steps.
This - this line is the part of your argument I find fairly bullshit.
There is nothing stopping Apple from making the same device, but giving you the keys to install your own software on it. Hell - They can even bury it in the settings, or lock it down through a provisioned profile so you can help your mom by turning it off if you're worried.
Instead - you're arguing that apple should abuse their position to keep other competition locked out. Because you think it makes you "safer". I don't think it makes you safer. I think it makes life easy for you, at the expense of everyone in the long term.
You have fallen - hook, line, and sinker - for the marketing of the richest company in the world, telling you "trust us - we'll keep you safe". You should ask more questions about why they need to do it this way. Why keeping you safe involves abusing their power.
That's the same safety China promises with their great firewall. Trust us - we'll keep you safe, happy, and ignorant.
Maybe that's a good deal to you - I think it's a shitty trade.