Practically speaking none of what you brought up are actually issues because once the phone connects to the internet once, it's unlocked forever, including after relocks/flashing. It's like saying you don't "own" the stuff you bought on bandcamp, because there's a split second between when you bought the song and when you could download it, therefore "It depends on a remote endpoint that can go down at any point, and depends on the company's policies present and future" and "It is functionally asking for permission to another party".

I don't think the bandcamp analogy applies. I may purchase a device with the intent of eventually unlocking the bootloader, but not doing so immediately for whatever reason, such as it still being supported by official updates, or the nth feature not being yet removed. Then the possibility of the option being taken away before you've exercised it remains.