I don't know precisely where the line is between owning the literal physical atoms and not owning the literal binary blobs of software, but agree or not, it's well understood that buying the right to use software is not synonymous with owning the software. I feel like the hardware–software distinction is a difficult one to square in the context of "owning an iPhone."
Does owning the atoms of your phone entitle you to a mechanism for side-loading your own operating system binaries? I think so. If you buy hardware, there should be a reasonable mechanism for wholesale replacing the supplied operating system software with any alternative you like. Should Apple be required to document how any of hardware works? On that I'm ambivalent but I lean towards yes. But as for how iOS works, I personally think that's regrettably out of scope, because owning the hardware isn't the same as owning the software.
I disagree - the restrictions also apply at the hardware level. The entire boot process is locked down to prevent people from running their own OS on the hardware. It's nothing like Macs where Asahi Linux exists as an option. If anyone ever discovered how to bypass the restrictions you can count on Apple to fix it.
But it’s pretty unambiguous that any restrictions are software, not hardware. It’s just lower level software that runs earlier in the boot/system bring-up process.
We're not powerless serfs, we can change the rules and we do it all the time.
There's also the location issue. DMA forced Apple to make some changes but only in the EU. Apple is willing to do the work to only comply in regions where they have to. What happens if your country decides that Apple isn't doing anything wrong?
If this is something you care about then you should not buy an iPhone. First change the rules and then buy one when they comply.