In the sterile conditions of a duel you are hardly discovering which pilot can really fly their craft better.
Besides, most duels are done in the same craft, to make it more of an even keel for the fight.
So, for duels, it doesn't matter.
For other situations, you might as well fly with 25% fuel, if you're so concerned. You'll save a LOT more than 200 lbs.
Then again, same goes for every plane in the game. You want to fly super-light, you have to pay the price (fuel supply). Doesn't matter if the P38 is 200lbs lighter than the one next to it, because the one next to it could have a lot less fuel, or the spit it's up against could have full fuel and a full slipper, who knows?
I'm just saying, it's a drop in a very big bucket.
EDIT: I'm all for fixing modeling bugs. If it's presented as one. However, I don't think it'll give anybody an edge, if it were fixed. Not any more than firing off the tail guns on the Bf110G (40lbs on a 15000lb frame) or the MG17 ammo on the 190a (170lbs on a 8500lb frame). It's just placebo effect.