You should probably only use kills, not kills-to-deaths, to rank the planes. Why? Well the majority of newbies gravitate toward the LA7, for example. Being new they will all die 90% of their sorties. However, before they die they will give the LA7 more kills than any other plane (hypothetically).
So the fact that folks ditch all the time, run out of gas, or die because they fly stupid, seems to give it a low K:D, but that's not really the point. Put one into a furball and it will most likely get the most kills and be the last man standing.
Also please keep in mind the LA7 was the HIGHEST killing plane since it was introduced. That's many many many years. N1k2 was second for many many many years. Only with the introduction of the Spit16 did it have a competitor. Every other plane was significantly behind the top3.
The only reason this may have changed recently is the splitting of the arenas, the ENY adjustments, and ENY limitation rule changes.
The La7 was the top killer in AH since... forever. Keep that in mind. It still is the top killer, but recent changes monkeyed with the stats/plane usage.
EDIT: And the field ack increase. No longer can a lone LA-7 pilot vulch as many kills with the thick wall of ack. Nor can it pork the field single-handedly, which is why the P51 with its 2k bombs and rockets has had much increased numbers, methinks.