Kinda found out that its the pilot not the plane..
In that case I should have roughly the same K/D in every fighter
But somehow I just can't get the same K/D in A Hurri I or C205 as I can get in a Spit XVI or Tempest ...

It's not
only the plane - but planes are our tools of the trade, and some tools are better / easier to handle then others. A good craftsman can overcome the limtiations of having bad tools, but only to some extend. Same as a very bad craftsman cant really benefit from having superior equipment.
But when having two pilots of some good & similar skill level, the differences of the respective planes may very likely decide the outcome of a fight.