Heavy bombers is not that unballanced in land fights even without AA-gun.
If you record punch/cost the Heavy bomber (assuming the bomber costs 12 points) 8/12=2/3, which compared to the artellery (1/2 or 3/4 if you count support) and tanks is not that insane.
But in sea battles, HB is realy powerfull.
What I think is strange is the repair IC technology. For Japan, Italy and US its definitivly totaly useless as the most probably will never ever get bombed at all, and it is probably useless for UK/russia too as I dont see Germany wanting to build Bombers instead of cheap land-based units. Its only germany which can ‘benefit’ from this technology and that only
if UK/US bombs them.
So my geuss is that this is one of the ‘wrong’ technologies.
The improved production might be realy fun in special situations. For Japan it is definitly nice. For US & Italy it is probably totaly waste. For UK it might be nice, but only if you at the time you get it have build a few extra factories. For Russia it might be neat to be able to crank out land-units closer to the front. Likewise it might be nice for the german player, but only if he is capable of holding one of the factories in Russia.
So in genall Improved production is useless for 2 countries, might be handy for 3 and wonderfull for japan.
Radar is likewise neat for Germany (killing fighters and bombers when the allies invades france…) but useless in extremly many situations.