Is it just me, or is the operational integrity Air doctrine the most valuable? So many things depend on air superiority in this game, Naval invasions require air superiority, Nuking and bombing requires superiority or is very costly respectively. I feel like the doctrine that boosts your fighters the most becomes more valuable as a result, both offensively and defensively, and operational integrity has by far the most bonuses to fighters.
Battlefield support gives in total 80 percentage points of various bonuses to ground attack missions along with 20 agility to CAS for survivability, at the cost of having only 30 points bonus to fighters compared to 80 for Operational Integrity. If you think you can win air superiority without the extra punch from Operational Integrity then an air force with Battlefield Support doctrine can absolutely flatten any opposition on the ground. Perfect for Germany and maybe Italy who will usually have Air Superiority in their mission areas. USA and maybe UK can benefit from Strategic destruction, for most others I agree with you that Op. Int. seems the best overall choice. With this doctrine minors can beat up the air forces of their neighbors and France can possibly vie for Air Superiority if they forego tanks, grounding the Luftwaffe's Battlefield Support. I'm curious to see which air doctrine, if any, gives the most benefit to carrier operations.