I think that the RPG is a bit overpowered. All you have to do is have an RPG (easy to get in wasteland [my favorite game mode]) and anything you lock onto has NO CHANCE of survival. I think you could make it more balanced by adding flares to helicopters but you can only deploy them every X seconds. There should also be some kind of warning sound that there is a heat seeker fired at you while in a heli so you know when to deploy the flares.
To make it balanced you should figure out how long it takes to reload RPG and fire it so many feet and decide how long it takes before you can deploy flares again.
For the armored vehicles i think there should be some kind of similar counter measure on them as well.