I though scrambling properties were limited and only really functional in factory zones if enemy wants to bomb. I used to implement air features intensively just didn't go well.
If one AA provide 1/6 hit change then why would two AA still provide the same AA stats while two of any units are always more valuable than single ones? Of course if 2 AA provides 1/3 change it would be overpowered but each additional AA can still increase AA change with lowered benefits.
An AA unit on the sea would be nice. The same can be said for land units that may perform AA abilities just I mean there could have been more variety of AA units.
If I make cheaper naval units then I should have also make cheaper air units too to maintain balance but it would ruin cost balance between land and air units. Convoy zones are nice but the problem is for example as Germany there is no way to take these incomes even temporarily without totally eliminating the British navy while in land warfare, if enemy is so strong you can just go around but the same cannot be done on the sea.