iirc there are doomsday weapons implemented by some mods (ISB for example) and they are just fine for my tastes - very lategame and very expensive tech, then very expensive build cost and so on.
but unless you think about diplomacy there is really nothing else you can do to balance it. you build doomstack + 1 planet killer. and wipe the whole galaxy (well...maybe energy cost of destruction (basically like terraforming a planet into the tomb world, while killing everyone on it may slow you down a bit...but in the end game you'd probably won't even notice)
but unless you think about diplomacy there is really nothing else you can do to balance it. you build doomstack + 1 planet killer. and wipe the whole galaxy (well...maybe energy cost of destruction (basically like terraforming a planet into the tomb world, while killing everyone on it may slow you down a bit...but in the end game you'd probably won't even notice)