I would like to know if it's even possible to build a Planet Killer without having traded a ton with Traders. In my personal experience, I don't see how you could. Even maxing out Advanced Mineral Collection, a non trader doesn't generate nearly enough RO from mining.

On the surface this seems like a major imbalance. The Trader achieves its win condition by doing what traders do, and ultimately can "force through" the win with skills like Blockade Running without having to rely on the kindness of others. The Warlord is oddly completely gimped with regard to its win condition without a LOT of help from traders. The Researcher isn't quite as bad off since its "win mobile" is much less expensive.

I agree with the suggestion above that Warlords need some other ability. I would propose that they can build all the way up to dreadnoughts with no RO cost. At least then they can build some scary fleets on their own and rough their way up to more resources under their own power.