I've come up with one more idea... or rather this time it's a bit of knowledge
Regarding aircraft, the best german aircraft during WWI was never the Fokker triplane (DrI) sure it is immortalized by von Richthofen, but he actually only scored 16 of his official 80 (unofficial 83) kills in that machine.
The best german aircraft would rather be something like the Fokker DVII (a biplane). This plane though was developed quite late in the war.
To sum up when different sides had the advantage through WWI, in terms of superior planes:
In the beginning of the war (1914 to mid 1915) there wasn't really any serious fighting going on in the skies.
From mid 1915 to roughly late 1916 Germany had a huge advantage, they developed the Fokker monoplane and the syncronized machinegun (firing through the propellers), both which caused huge casualties on the allied airforces. These planes were initially flown by aces such as Immelmann and Boelcke.
During most of 1917 the allied (France and Britain) had superior aircraft and they had a big advantage.
In the late stages of the war, the two sides were more equal, in terms of aircraft quality.
This is how I remember things, they might be slightly off, but the general trend should be correct
Perhaps these changes could be implemented in the techtree ??
I think that a tech "syncronised machinegun" should be made available.... and that it could have some sort of prerequiste tech which only the germans have, to emulate their coming advantage
With that tech, the germans should be able to build Fokker monoplanes (which should be superior to allied planes of that tech).... when biplanes are invented the allies should have superior planes... triplanes whould yield aircraft that have a bit shorter range (to emulate that they where much slower than biplanes) and a lower defense value (since they cannot outrun biplanes)... I suggest that a "advanced biplane" tech should be made available, where the germans finally catch up with the allies and get, for instance, the Fokker DVII
Hope this is useful