There's not much proving P-63s managed to fight anything that wasn't a GV or wearing boots.
That doesn't make the plane less importance, fact is both the luftwaffe and Japanese were done with when it was introduced. What if a plane was introduced (P-80 just for an idea), flew combat missions but did not manage to get any kills in a month? does that mean it didn't serve in combat?
We can argue its importance in the war, but facts are the P-63 served in combat.
A soldier in 1945 had just as much of a chance to get killed than in july 1944, does that mean he did not serve combat either? Why not? he might not have gotten anything to shoot at, but maybe he picked up that german helmet and tripped a mine instead. Do we discount his war experience just because of it?
Just fuel for thoughts, the war isn't over until someone surrenders.