Imagine an AH with no spit16, no spit8 (nearly identical, those two). Now look at this late-war spit that climbs almost 5000feet per minute. It zooms like almost no other plane in the game, can climb like a 163 (probably better at certain alts!), and has 2 hizookas and 2 50cals.
Now tell me why it would NOT be perked?!?!?
Then introduce a spit16 that can match this climb rate, this armament, but also surpasses it in turning, handling, and roll rate.
The question isn't "why is the 14 perked" -- but "why isn't the 16?"
EDIT: As a follow-up, the handling alone isn't grounds to unperk something. The potential is there, just don't screw up when you fly it. Same goes for a 262. Same goes for a Tempest. Same goes for a Chog.