[Malorn]

I haven't heard anything saying that main gun (driver gun) is the strongest.

What I have heard is that the secondary guns are "no joke".

I think it's reasonable to conclude that in order for the secondary gun to not be a joke it needs to be significantly better than the primary gun in whatever role is chosen (AV/AI/AA), otherwise you have absolutely no reason to man the gun over pulling another tank.

I expect the main gun will be a general "all purpose" AI/AV gun, but not super effective at either. As in, it'll take many shots to blow up another tank and it'll probably take multiple shots to kill infantry. By comparison a mortar on the top of the tank will be far more effective against infantry, making it more worthwhile than running two tanks - IF your purpose is infantry suppression.

By my rough expectations, I believe the secondary gun needs to be at least 2x as effective in its role over the main gun in order to justify the resource cost of the upgrade and the opportunity cost of not having a second tank.

So if you had 1 tank with a mortar secondary gun (AI config), it would be roughly as effective at taking out infantry as 3 tanks w/o gunners. Likewise, a tank w/ AV secondary gun would be 3x as effective at taking out tanks.

If that isn't true, then pulling a second tank will always be a better choice.