With existing planes we have I doubt adding these planes won't take that much effort

Luftwaffe
bf109e7 (post variant battle of britain bf109e that saw action in opening months of Barbarossa and North Africa)
bf109f2 (a bf109f4 with faster-firing 15mm MG-151. Was this variant WEP-less btw?)
bf109g6as (later varient 109g6 with slightly higher altitude performance, 30mm MK-108 nose tatter option added)
bf109g10
fw190a3 (early war fw190a)
fw190a6 (mid-late war fw190a)
fw190a9 (late war fw190a with 2000hp engine)
Red Army
i16 type 18
la5F
p39N (soviet ace Pokryshkin's favorite and saw most important actions in 1943)
US Navy
f6f3 (WEP-less, mid war variant of late war F6F-5)
US Army
p38h (fills gap between p38g and p38j
p47d-5 (pure mid war razorback p47)
p-51a (allison-engined mustang)
RAF
spitfire 2 (a great matchup against bf109f2)
spitfire lf5 (a spit 5 with chopped wingtips, higher engine power suited only for low altitude)
spitfire 12 (would be nice as a perk plane in mid war arena, basically a spit with clipped wing and detuned griffon engine from spit14)
Fleet Air Arm
seafire lf3 (basically a navalized spitfore lf5)