the problem of that is.....that a zitadells count.

Overall that is  bad balance....

it would be much better just to allow to build one "Planet Destroyer", one "Moloch", one "Zivil Version" (for Terraforming ect),

Out of the military Version you build the Planet Destroyer or the Moloch.

Remove the Leviathan need for building a Zitadell and simple build it on the planet you want to have it.

First you have to build the K3 Building + a Spaceport (think level 3 should work fine) doing the research ...and than you can start to build the citadell...

Give the K3 Building not a x2 cost....let it cost XXXX Dust and give the Citadell also a normal Upkeep.

I speak german so sorry my english is not the best to explain it.

So the Cost explode should be no problem anymore...and it is balanced