it has always been confusing, I upped an F4U-1C one time, paid 13 perks for it, I shot down 9 planes....and when I died, it had cost me something like 18 or 19 perks........figure that one out..........one would think in killing La-7's spit V's ( before the Spit V change ), etc etc......
that some of them kills would have offset the perk cost at least a few perk points.....but it does not.....
but is just another part of the games mechanics..........this is hitech sandbox.............you don't like it........you will probally be told to go find your own sand box and build your own castles........ just saying........