This is a very complex topic that is very hard to draw the line on.
As a technical person who follows hacking and security news i can understand google introduced the api and warnings, as phones are getting hacked and unlocked bootloader or root can be abused to keep your malware going, and has been abused in the past.
But as a user of fairphone/lineageOS, who tells google, apple, meta, … all of them to fuck off when i can, this scares me. The lockdown of devices can and is going too far. Hell, i even consider samsung’s android ui changes to be going too far, as it changes a shit ton of stuff and really is not a stock android experience. It locks users in their environment…
Pre-locked bootloader times ive had multiple android devices be passed to me that were malware infected that changed the rom in a way that even a factory reset would not remove the malware. Locked bootloaders made it so the rom needed to be signed and unaltered on boot, fixing this. Root access also means apps can use and access api’s in android that it normally cant, changing settings and things inside android it shouldnt. What do you think happens when malware comes in? :p
Imo, i agree what you said. bootloaders should remain locked but you should be able to somehow, in the bootloader, be able to add the os’ signature/keys to the bootloader’s trusted stuff like how secure boot on a pc keeps os signing keys and verification stuff inside the tpm.
This way you can install lineage os for example, tell bootloader to trust it, and lock bootloader again so nothing can be changed anymore.
I wouldnt take this from user input, as that is controlable by malware, but rather come from the OS itself. Maybe even during installation, idk