So after a little research, a civil war cannons range was around 1,523 yards, that is around 1392 meters, that is with the limited understanding of gun powder and metallurgy that we had in that day and age, with the refinements we more then likely made sense we are on another planet it is safe to say that we should easily be able to at lest reach 2000 yards even with our standard tank shells in game.
So yes, the tank cannon's range is total shit!
[I mean come on! we have flying robots!]