Your stats don't match your conclusions fats. You have killed more spits and 51's only because there are more of them in the arena. I'm not surprised your kill numbers match the ratio of how many fly each plane.
You are a veteran.. experten in the 190. You graze on the dweebs, and the dweebs fly the P51 and Spit more than any other planes.. therefore your kill ratios are better for those planes.
Mine look like this:
Lephturn in P51 vs. Plane Type
14 to 2 vs P51
6 to 1 vs 109G10
18 to 3 vs Spit
5 to 0 vs Macchi
13 to 1 vs 190A8
3 to 1 vs George
2 to 0 vs Chute (hehehe)
1 to 0 vs La5
Now I haven't flown nearly as much as you have, so my numbers aren't as representative. However, observe that the 51 and Spit top my list as well. Not surprising. Oh look.. the A8 ranks right up there... OWMIGAWD, it has the worst ratio!

Now you see why I love to see a lower 190?

All these stats show is how many people or dweebs fly a given plane, and not much else. IMHO
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Lephturn
The Flying Pigs