Ok, quick statement here...
109K4 has a 30mm cannon with a low ammo count at 60 rounds that the majority of pilots in AH dont know how to use properly. Spit14 has 250 rounds of 20mm Hispano (if i recollect, is the most accurate 20mm in the game?) and 2 .50cals at 500 rounds, the 109k4 (has 7.7mm mgs in the wings correct?).
Spit14 has near equivalent speed and climb rate but has anyone thought of acceleration? Whenever i fly a sporkteen at 15-20k, i go from 200mph to 350 very rapidly. It also out turns a 109K4 too.
The 14 dives as well as a 109K and possibly even better (yeah, the roll rate is poor because of its elliptical wings but ive never seen this as a major problem when im diving on enemies).
Sporkteen is perk worthy. Just learn to fly it. I've started flying it lately in the MA and i haven't been opposed evenly by any aircraft at level alts. Even when against 3 P47Ms and a P51D with them 5k above with my sporkteen and 2 P51s below them, i took out 2 of the 47s and then killed a low flying F4U1D with one of my squaddies taking the 51 and the other 47 out. Not bragging, I'm using this as a point. I'm learning the plane and it seems easy to fly (maybe because i fly 51s? the 14 seems to be like a 51 sometimes).
Edit: you also need to remember that alot of noobs or fresh pilots will use the spit14 expecting it to fly as well as the 16 or better due to the perks. i have a feeling that many pilots think, its got perks, so everything about it is better than the other models. This would include turn rate, speed, ammo, climb rate, dive capability, etc.