Yeah, it takes two to go to war. If Poland didn't want to go to war with Germany they could have just said no.
They didn't find the founders in the first two years because the founders didn't want to be found. Their MO in the gamma quadrant is to be hands off most of the time then to send in the Jem Hadar to blow people up when they get mad. They didn't put any territory markers on that planet because it doesn't concern them to kill solids. They tried to find evidence of the Dominion that all the aliens kept referring to but couldn't find them anywhere. They also didn't destroy the wormhole because they thought it would always be an option. Remember they were attempting to do so when the Dominion made it impossible.
Being a prior victim of atrocities is not an excuse to commit atrocities of your own.
Odo didn't convince the female changeling that humans were ok afterall. He convinced her that they would not try to murder them all in revenge. The war was already won, Odo just convinced her to give the order to surrender rather than fight to the last man. It wasn't Odo or the bioweapon that won the war, it was just Odo that made the victory less bloody.