Basically, the thing is, a cruiser is no match for fighters/bombers.
Well, if a cruiser can take on four wings (16) assault fighters, it's doing a lot better than a real life cruiser would...
If 10 cruisers can take out one fs2 fighter their doing a lot better than a real life cruiser. Read: Fury = several kilotonnes
Would a bgreen or an ultra-antifighter-beam take more energy, because you could have an orion, replace it's BGreens with UltraAAAs and clear the reactor space out for fighters or channel the remaining power into a forward LRBGreen that's designed to be overcharged.
Strap 4 mjolnirs onto a large asteroid, slap on a couple of engines and a jump drive and you have a strike craft. Or have outerspace bunkers made of huge asteroids with a reactor at their center that powers a bgreen and have them floating around in space for a sath to pound away on while a GTVA fleet attacks it and provides fighter cover.
You could spread out through many, many, many systems so losing a couple to supernovas and planet bombardment does't matter so much. But you'd have to have a fleet too to stop them spreading too fast.
Blow up any node you see and rely on traversing space very slowly rather than subspace.
Or you could use the money for the colossuses, frigates, upgrades, corvettes, carriers, fighters, bombers, meson bombs, destroyers, personell, mjolnirs, etc. for having a good time because you think they're gone for good or you believe your doomed if the shivans come again with a greater force anyway.