... another very big improvement would be to deprive AI from their current stock advantages, such as:
It's simpler to make AI all seeing and all knowing. Realistically, the opposite should be true. Realistically, "elite" units are only elite because they screw up less than "average" units. Furthermore, during WW2, the average standard of flying skill, gunnery, etc. was shockingly low, due to some combination of lack of time and resources, or faulty training doctrine. During WW1 it was even worse. For post-WW2 conflicts, things got better, but even well-trained pilots equipped with the latest technology can still screw up, and history has shown that, even with the best training, most fighter pilots are victims waiting to happen.
Aircrew should be blind to the enemy by default. They should be assumed to be lost by default. They will avoid contact with the enemy by default. They will avoid any form of risk to their planes (e.g., breaking off missions due to mechanical failure or bad weather) by default. They will have less than full mastery of their plane/equipment until they reach a very high level of skill.
Regarding AI skills there are currently 4 levels in stock game in scripted missions/campaigns, ranging from noob to ace (skill 0 to skill 3)
Skills should be rated from 1-100%, or some variation like 1-10, with most aircrew having skill levels of 30-50% (3-5). Pilot skill should be expressed in terms of pilot hours and possibly hours in type. Combat experience should be expressed in terms of combat sorties or hours of combat flight. Factors like injury, fatigue, pain, fear, g-forces, and hypoxia should negatively affect skills in most areas.
At the very least, you want to break out Piloting, Navigation, Gunnery, Equipment Operator, and Ordinance skills. If you want to get fancy with the basic skills:
Piloting: IFR, Aerobatics, Combat Maneuvers, Single-Engine, Twin-Engine, Multiple Engine, Glider, Seaplane, Vertol, Autogyro, Low Altitude/NOE, Fuel Conservation, Rotary Engine, Radial Engine, Inline Engine, Jet, Rocket, Turboprop.
Navigation: Dead Reckoning, Celestial Navigation, Radio/GNSS navigation.
Gunnery: Fixed gunnery, Flexible gunnery, Turret gunner, Gunnery computer (e.g., the gun targeting systems on the B-29).
Equipment Operator: Radio, Electronic Warfare/ECM, Sonar, Radar.
Ordinance: Air-to-Air Unguided Rocket, Air-to-Ground Unguided Rocket, Bombardier/Level bombing, Glide bombing, Dive bombing, Skip bombing, Bouncing Bomb, Heavy Cannon, Torpedo, Guided Bomb, Guided Missile, Guided Torpedo, Aerial Mine, Cargo Dropping, Paratroop Dropping.
If you want to get into "role-playing" aspects, you can do things like rate aircrew by things like Strength (necessary to manage heavy controls, force open hatches, etc.), Reflexes, Health/Fatigue, Aggression/Courage, Morale/Stress Tolerance, Eyesight, and Situational Awareness. Possibly have a stat for Luck as well, since there does seem to be an element of luck which explains the survival of certain pilots.