Your fallacy is assuming kill/death ratio is related to the aircraft's performance itself. It is not. The spit14 is perked for good reason,
No it is not. Absolutely not. In this case the (relatively) low K/D reflects pretty much the aircrafts performance. Many factors that can artificially affect the K/D of a plane in a negative way are simply not present. No 2-week noobs augering čn masse (perk barrier). No porkers using it for suicide jabo runs (no ords), like the 47N or 51 or 38L. No one ever offered any explanation for it's low (for a perk ride) K/D
Fact is, the Spit 14 is a good & capable plane, but it offers nothing in LW MA play that puts it clearly "above & beyond" it's opposition in a manner that could be even remotely described as "unbalancing" in any way. It's still fragile, it actually does not like high speed (roll rate being quickly reduced to almost zero), it's an unstable gun platform with some vicious stall characteristics.
It's fast at MA combat altitudes - for a Spitfire, overall it's just "quite good". It climbs well, but 109's to that as well (and have 10mins WEP).