My Lrg train has all gunboat turrets and everytime i fire, my energy goes down by 2 blocks. Yes, they are powerful but i dont think that they are unbalancing because they use alot of energy.
Also my train is meant to inflict as much damage as possible in a short time, perhaps to make the enemy retreat or to distract him while i try to escape.
its not like i want to fight when im in my train but i think my energy will be nearly used up by the time i escape. That means maximum damage in a minimum time.