I'm sorry, what does that have to do with anything? Quite simply, this idea punishes *anyone* who flies the P-38J simply because many good pilots are putting up numbers in it, and rewards *anyone* flying a Spit16 because it is flown by many inexperienced players. I can't believe you think that on given sortie one should earn less perks for flying a P-38J, simply because so many good sticks fly it. And let it be known, the main reason it gets flown instead of the L is because it has cooler skins!!!
And to really drop the silly penny in the stupid machine, one could fly the slightly superior P-38L and earn many more perks.
The problem with your way of thinking is that you try to prove that it fails in terms of a certain single sortie approach (which it does, but more on it later) while I think it will work on a whole, thousands and thousands of different sorties considered.
Lets stick for the P-38J / Spit16 comparison.
You think the strict K/D ratio would reward pilots flying the 16 and punish those who fly the -J. And yes, you are right, ist does. So why is this ok?
As you already stated many good pilots push the J up the ladder, while many bad pilots pull the 16 down. This is the very standard of the LWAs and I think on one can deny this. So, should the experienced pilot in the J (arena standard) get many many extra perks for beating up a noob or a poor pilot in the 16 (also arena standard)? I say no, because it's easy and easy kills should not be rewarded. Should the bad 16 driver get lot of perks for killing a good stick in a J ? Definately! Simply because if he manages to do so, it must have been a hell of and effort, or the 38 driver screwd up - in both cases, well deserved perkies.
I can see you now arguing what would happen if 2 similary skilled pilots (non arena standard) have a go. Then most likely the Spit will be the winner and gets massive perks for a easy kill. Yes this will happen once in a while, but not on the vast majority of encounters, where the skill levels differ widely. So while it may fail in the smallest possible event, it will still work well as a whole.
But, lets say, for some strange and very unlikley reason, all of a sudden, only similar skilled players fly both the 16 and the J - then the sheer beauty of K/D strikes yet again:
It balances itself all the time.
In a situation like above, the Js K/D ratio will go down just as quickly as the 16s will go up, reversing the situation. Now the superior plane has the lower ENY, just as you think it should have.