Here are what I think are the relevant statistics. I listed all the perk fighters because the Spitfire Mk XIV is perked and should be compared in kill/death ratio and usage with its fellow perk fighters. I selected the unperked fighters by picking high usage, powerful fighters that, with the exception of the La-7, tend to draw more experienced and better players to them. I think that using this selection of unperked fighters is fair as the people that tend to fly perk planes tend to be at least moderately experienced and to fly in a more conservative manner. I included both the post-perk Ta152H-1 and pre-perk F4U-1C as a comparison with the Spitfire Mk XIV's current performance.
Late War Tour 96, 1-01-08 to 1-31-08
Perked fighters in order of their kill/death ratios:
Tempest has 6136 Kills of All models and all models have 945 Kills of Tempest. 6.49 to 1 kill/death ratio.
Me 262 has 4103 Kills of All models and all models have 698 Kills of Me 262. 5.88 to 1 kill/death ratio.
Me 163B has 790 Kills of All models and all models have 160 Kills of Me 163B. 4.94 to 1 kill/death ratio.
F4U-1C has 9910 Kills of All models and all models have 3875 Kills of F4U-1C. 2.56 to 1 kill/death ratio.
F4U-4 has 2754 Kills of All models and all models have 1256 Kills of F4U-4. 2.19 to 1 kill/death ratio.
Spitfire Mk XIV has 1454 Kills of All models and all models have 1139 Kills of Spitfire Mk XIV. 1.28 to 1 kill/death ratio.
Unperked fighters with high kill/death ratios and medium to high usage, in order of their kill/death ratios:
Bf 109K-4 has 9344 Kills of All models and all models have 5981 Kills of Bf 109K-4. 1.56 to 1 kill/death ratio.
Typhoon IB has 17053 Kills of All models and all models have 11094 Kills of Typhoon IB. 1.54 to 1 kill/death ratio.
Ta 152H has 2999 Kills of All models and all models have 2042 Kills of Ta 152H. 1.47 to 1 kill/death ratio.
Ki-84-Ia has 9016 Kills of All models and all models have 6224 Kills of Ki-84-Ia. 1.45 to 1 kill/death ratio.
P-38J has 6562 Kills of All models and all models have 4525 Kills of P-38J. 1.45 to 1 kill/death ratio.
Fw 190D-9 has 13943 Kills of All models and all models have 9865 Kills of Fw 190D-9. 1.41 to 1 kill/death ratio.
La-7 has 33201 Kills of All models and all models have 26480 Kills of La-7. 1.25 to 1 kill/death ratio.
F4U-1A has 6568 Kills of All models and all models have 5381 Kills of F4U-1A. 1.22 to 1 kill/death ratio.
Tour 15, 4-01-01 to 4-30-01, the final tour with an unperked F4U-1C:
F4U-1C has 27717 Kills of All models and all models have 20022 Kills of F4U-1C. 1.38 to 1 kill/death ratio.
What do these statistics tell us? One, the Spitfire Mk XIV has, by far, the lowest kill/death ratio of any perked fighter. Two, the Spitfire Mk XIV has the lowest usage of any perked fighter save the Me163, and that is limited to one base per country. Three, unique among perk fighters, the Spitfire Mk XIV has a lower kill/death ratio than many unperked fighters. Four, the perked Spitfire Mk XIV has a lower kill/death ratio than the recently unperked Ta152H-1. Five, the perked Spitfire Mk XIV has a lower kill/death ratio than the unperked F4U-1C did despite the fact that the F4U-1C was at the time, by far, the most popular fighter and was used by more unskilled players than any other fighter.
What do I think an unperked Spitfire Mk XIV would be like? It would probably see higher usage in Spitfires than any of them other than the Spitfire Mk XVI and Spitfire Mk VIII, though the Spitfire Mk IX might also see heavier usage. It would probably have the highest kill/death ratio of any Spitfire. I doubt it would be a popular fighter after the initial "Ooh, it's free!" period had worn off and would instead find a solid place in the second tier of fighters used by more experienced players who can manage the quirks of these fighters. It does not handle like any other Spitfire and would be offputting to most casual Spitfire users.
I think the Spitfire Mk XIV is a good fighter, but nothing worth spending perk points on. As such, it should follow the Ta152H-1's example and be unperked.