The other thing one has to remember is that we, in the future, have the benefit of hindsight knowing that the axis failed to develop something to counter either of the 2 a/c (mkV/IX vs FW190 not withstanding). At the time the powers that be had no such luxury so it was probably wise to keep all the arrows in one's quiver (so to speak).
As an example, the mossie relied on speed for defence. If that then is the main problem for the axis, and they develop a radar-equipped jet-powered night fighter, then, politely, you're buggered and have nowhere to go. By having a full spectrum of aircraft you give the enemy a variety of problems to counter and something to fall back on yourself.