When you complain to the DVLA you need to keep your complaint ENTIRELY focused on the fact that MET Parking issued you with a PCN which stated PoFA keeper liability at a site where PoFA does not apply.
If you include extra elements to your complaint then DVLA will spend a side of A4 drawing your complaint AWAY from the crux of the issue - in other words, you'll receive a 'fob off' in response.
I'll lay odds now that your Stage 1 reply will be a reply that both explains how PoFA works and never addresses your misuse of data claim against the operator.