I'm seeing some a few things that seem counterintuitive...
The P-51D's KTD, despite being possibly
the newb ride. I'd be interested to know what percentage of pilots flying the P-51D have an overall KTD greater than 1; it seems either the newbs are getting better, or more vets are taking the pony out for a spin.
The A8 has a higher KTD than the A5, despite being inferior at typical combat altitudes in just about every measurable paramater. Its useage can be explained by the fact that it has better guns, and that 8>5 and therefore the A8 must be better
.
The 190F8 appears to be in the top half of fighters based on the numbers, which seems odd, given the fact that its about as agile as a school bus, and doesn't account for that great of a percentage of air to ground kills.
In general, there appears to be a loose correlation between useage and KTD. Whether its the useage affecting the KTD (and one would think that the more Joe Derp gets behind the stick, the lower the KTD would go), or if the higher KTD fighters draw more playes, I'm not in a position to say. Lusche, can we get a trendline put in?
Just a few other things I noticed, the P-47M has pretty much entirely replaced the P-47D-40, which is a bit suprising to me, since I've always kind of felt they were inferior as pure fighters. I mean while I know theres a few sticks out there that can make them shine, they were always near the bottom of my threat assesment list.
Also, the P-38L seems to be kind of a crappy fighter, just based on its possition on the chart, while the near identicle P-38J has close-ish to the same useage, but has a KTD greater than 2, instead of less than .75. Just illustrates how big of a difference in the overall numbers that a relative few good pilots can make.
P.S., You made a typo, the Spit 8 (presumably the Spit 8, anyway) is listed as the Spit 7 on your graph.