also what about redundancy at these insane sizes?

https://xkcd.com/1737/

Capitalists now: “Here is your 26 megajoule cupcake!”

Capitalists a year later: “Here is your insulin subscription, only $299/month!”

Yes, that can happen sometimes, but I find that there are plenty of cheap options with unlocked bootloaders if you look for them.

Nah, cheap phones often have their bootloader unlocked/unlockable. Really happy with my POCO M5 running modified AOSP. Also, unlike every expensive phone nowadays, it has 3.5mm jack, SD card slot, and exceptional battery life for hiking/trekking (it survives 5-6 days as just a camera+map phone with all power saving on, in comparison people with flagships typically only last 2-3 days with the same usage and power-saving techniques).