I have noticed that they are able to fire through mountains and other land formations. I think that this is a dis advantage to attackers because if the gun is completely surrounded by mountains bombers and even land units can not attack them. The range is good for sieging the base but the bullets need to be stopped by terrain.
This is still the alpha, the collisions of object on the planet may not be in yet so this is still to be done. Its got nothing to do with them thinking its fine the way it is, its just not finished yet.
I've had t2 nukes just hit mountains because they're in the way. But artillery does aim up and over.....
Yes, if you view it at the right angle you can see that most artillery, including the bots and vehicles usually shoot waaay up, then let it arc down.