One thing made no sense to me though.. Why did the woman shapeshifter order the destruction of the Cardassian city when they were depending on the Cardassian military in order to have any chance of defeating the Federation/Klingon/Romulan Fleet. Surely that is a monumental blunder, and if she/it hadn't given that order it's likely that battle (and the war) would've had a totally different outcome..
They weren't counting on the Cardassian military to fight off the Allied fleet, though. The Jem'Hadar were going to do that, by themselves at first. The Breen commander had to convince her to let them stand beside the Jem'Hadar. The only contribution by the Cardassians were the unmanned weapons platforms.
Besides, the Cardassian people had shown themselves to be disloyal to the Dominion, so the need to eliminate a threat behind the lines was judged to be more important than maintaining a few loyal Cardassian ships and commanders.
I mean they were concerned about a full on Cardassian uprising and then they go and do the one thing that absolutely guarantees that every Cardassian is going to turn on the them.. Surely they know that the Cardassians are so proud they'd never allow an atrocity like that committed against their people to go unpunished.
No, they don't "know" the Cardassians would never allow an atrocity like that. Why would they? They never cared about the Cardassians. They were a foothold in the Alpha Quadrant, and no more than that. They didn't treat the Cardassians as equals even when relations between the Cardassians and the Dominion were at their best.