A weapon can be as powerful as the Death Star without having planet killing capabilities. It's simply a matter of how many guns you have on the thing and how many people you have to man them, along with the weapon's armor and speed.
As for what countermeasures there are to protect oneself, at this stage in development, we simply don't know. Point defense systems are a must, if missiles are ever going to be a thing in-game. Perhaps shields will be better at stopping lasers and armor at stopping kinetic/explosive based weaponry, as is the classic way things are divided. Until NQ tells us, we won't know. We can make suggestions though.