Flashing an unsigned (or potentially differently signed) bootloader burns fuses. Sure. However, other manufacturers don't just burn fuses, you specifically need to apply for permission to flash your bootloader e.g. https://www.oneplus.com/support/answer/detail/op588
Samsung at least don't require personal details for you to take control of your device. Sure, you lose access to some multimedia, but don't blame Samsung for that, blame Widevine DRM certification. Knox goes out the window, but the entire point of Knox is to (try) guarantee a device isn't tampered with. At least you can remove it!
well, Miami and one plus requires you to provide phone number etc., so that seller and other people don't sell you malicious second hand phone or tampered phone. However, there are no fuses, so your phone will still be on warranty if you unroot it.
What does “tampered with” mean? Particularly in the context of a device you own?
I would consider a device tampered with if someone besides me (the owner) did something with it, without my authorization. But anything short of that is surely just me using the device. I mean, I have physical possession after all.
Signing images and requiring that the bootloader can't flash anything else is just vendor lock in / ceding your power as an end user. It doesn't make you more secure in any way since a bad actor will figure out a way to bypass making writes to the system partition.
Umm I remember ordering Chinese phones way back when (think android 4) with unlocked boot loaders - both had some random junk installed via custom ROM and you couldn't uninstall it.
Samsung at least don't require personal details for you to take control of your device. Sure, you lose access to some multimedia, but don't blame Samsung for that, blame Widevine DRM certification. Knox goes out the window, but the entire point of Knox is to (try) guarantee a device isn't tampered with. At least you can remove it!