As someone who usually plays the Axis, I found that airborne units are insanely effective. You can pretty easily snipe places like Transcaucasia (5 IPP and aligns Turkey) with 1-2 airborne and some air support. It can get pretty dumb.
I would recommend that airborne units need to match 1:1 with the IPP value of any non-island territory unless the territory is being simultaneously attacked by your land units or adjacent to a territory being attacked by your land units.
Basically, this would reign in exploiting airborne (can’t snipe London, Moscow, Berlin, with solely airborne unless there is a tonne of them which is unlikely due to the nature of airborne troops.
I think this would be a simple rule to implement that would prevent cheesing.
Please feel free to critique this or add to it.