They can introduce a support unit that shoots at aircraft. The army will only need one (presumably) but it would work. Also fighters could always dogfight in the skies. May require increasing the number of planes you can have. And would mean bombers require escorts.
Additionally the Germans...
I literally just created a nexon account for this very reason. I do not see any need to limit tactics the way it just happened. It is absolutely ludicrous to do that. NEXON, go back to the old system please.