Dictionary definitions are not formal definitions, they are attempts to capture usage. And they are almost invariably approximations except when explicitly specifying otherwise, and outside of the the more lavish of the unabridged dictionaries are also almost in invariably simplified, both in the number of definitions of any term presented and often the individual definitions, for brevity at the expense of accuracy.
Yes, but to use a term in a technically relevant way, it needs to be tied to reality; if not, it's just marketing jargon or pseudo-tech speak. The best technical definition for this case is not by how it is most commonly understood, but how it most commonly applies. Dragonwriter makes a compelling case in that it is most commonly true that a user won't have access to the specialized hardware required to "unbrick" the device.
"Literally" is often used when the subject is metaphorical, but that's not the same thing as it meaning "metaphorically". If you took the "literally" away, it would still be understood to be metaphorical - the "literally" is intended to strengthen. It's the normal sense of literally, used hyperbolically.
In the same way, when someone says "you left me waiting for days" we don't say that "days" sometimes means tens of minutes.
From Dictionary.app that comes standard with the Mac: "a smartphone or other electronic device that has completely ceased to function"