Hail of bombs imbalanced

[Prog]

but if you are not flying you can be blocked by creeps, other tanks or the environment so you might not be able to get out of the bombed area

That's one of the reasons why a 4.5k gold air tank has 3600 hp and the 4.5k gold ground tank 4500 hp - even more than one additional hit from lvl 1 ultimate.

I just know one 4,5k air tanks which is the air ship and it has more than 3600hp
afair it has almost 4k (39~~) without hull

http://btanks.net/wiki/Air_Ship

Of course it has ~4k hp at lvl 10, because it gets +1%hp per lvl. But same goes for the ground tanks, they get even more hp/lvl becouse their base hp is higher.