Nooooo leave my rail guns alone! They are the only weapon I care about! Like in Masters of Orion 2, you can use Autofire Armor piercing Mass drives for 80% of the game.
Maybe just make their firing arc like 15 or 10 Degrees or something.
Regardless of their power, when you have a large map and up against ships with them, it's even Steven all over again. Besides I love their range. Speaking of range, their range seems lower on planet mounts than on ship ones.
But don't change them