I was wondering if I can make a full backup of my system partition via fastboot or adb and re-apply the backup to a different phone of the exact same model? Or is this only possible if the bootloader is unlocked? Right now it sounds to me that the locked bootloader only prohibits flashing a new bootloader or recovery.

The firmware being backed up would always be an official firmware.

My case right now is about a Sony phone but it would be good to know if this is something that's generally possible or not.