I had a really detailed and good reply to this but my ****ing mouse decided to click on the wrong damn button (one of these Microsoft super mice with too much technology and piss poor interface).
Long story short.
Download the mod, (if you haven't already), look at what the Germans actually get, think for a second about the fact that most post-war projects in aviation, rocketry etc were pinched German designs / know-how and ask yourself just why design "slackened" from mid 45 onward for a while. I'll give you a clue - there was no one left to catch up with.
If you want to close the tech gap vis-à-vis E-75 and up then one bright spark who is mean with a virtual paint-brush can knock out some "Kitty-Killers". I'll do the rest.
The German kit is almost all based on designs that were going to be introduced. The rest is extrapolation very much within the realm of balance (you need to have a point of reference when you design an AFV from scratch and have in most cases nix to go on and that point of reference is invariably other kit from other oobs) and realism.
If you like I could put in some flying saucers.
The Do. 407 is already in the mod. I included it because the mod is already too full with analogue designs when it comes to helicopters.