^It could play out that way too. Either way, the Cardies former homelands are footing the bill. You could call it "diplomatic plundering."
As for Septimus III, we do have a shortage of information. However, even if the Klingons planned to slaughter the entire Eleventh Order outright, so what? They're Klingons. That's kind of what they are known for. Hell, they probably had their opera boys write several epics about the battle. It's not something they're going to be ashamed about, and it won't be something that can be used against them at the bargaining table.
Of course the retort to THAT is, "I don't care WHAT your DNA structure is--that doesn't excuse the fact that you chose to commit an atrocity." The relativist Federation probably wouldn't have the stomach for such an argument, but the Cardassians strike me as absolutists from a moral/ethic standpoint and I bet you they
would say it.