Heavy artillery, drone carrier, I see them as kinda the same thing, but it's a fine line
Well, you can set the droner as the sight painter (have to use a special drone) and another char as the gunner, but really, what's the gunner gonna do? Just hit the button when the droner says "now?" I understand what you're saying, but who's gonna subject themselves to being the gunner in that case? It'd be no fun. (Or did you have another idea in mind?)
Now, if we can get the gunner to also pilot it, and make the veh fairly slow compared to other vehs, but not turtle slow, that would change things up. The gunner would run around the wastelands in random patterns while the droner kept telling him when to fire. That way, the vehicle would be harder to find, thus having bombardments coming from who knows where, and when they know where, it may have moved. Maybe the beam could have a moderate arc out of the sky so the people getting hit can see from what general direction, but not see the vehicle itself (which would give them some hope of finding the artillery.)
Ooh, and an idea... the drone that is used for ammo could stay put, just damaged beyond repair (could be salvaged for common drone parts or researched) and the opposition could pick it up, hack it, and then have the location of the artillery at the time of firing (not current, mind you, as that would be overbalanced and just plain dumb as the thing is now out of contact with the artillery and isn't functioning properly.)
And another thing, the drones would have to be fast.... very fast, to cover the distance from the artillery to the op (or wherever) to make the artillery viable.