I believe the EGC is the first line of defense because it doesn't need electronics that could potentially fail. GFCI's are a backup stop gap measure for compromised EGC's. My opinion, of course.
This is true for faults where the “hot” wire comes into contact with any adjacent metal.
The GFCI is still the first line of protection when a person comes into contact with a “hot” wire while also in contact with anything grounded.