I’d agree that the techs for Air units are overpowered, while Sea techs are underpowered. Combined that the increased size of the board and lowered cost of Bombers, and you have Air units excelling.
Lets compare
Air: Gets Heavy Bombers(Best Tech in the Game), Paratroopers(Powerful and Abusive), Long Range Aircraft(Powerful and Abusive), Jet Fighters(Powerful, but reasonable).
Sea: Gets Improved Shipyards(Ships cost 15-20% less, which won’t pay itself off until you buy 60 or so IPCs worth of Ships, and doesn’t boost existing Air), and Super Subs(which is useful only if you are able to use Subs).