In one episode Odo takes the form of the Female changeling to fool a Dominion crew. If Odo was capable to taking her form and imitating her, why didn't he do that more often? He could have ordered entire fleets to stand-down. Odo didn't even need to link with her in the finale, in order to convince her to end the war. He could have just imitated her. Once she was captured, Odo could have pretended to be her and ended the war.
Also, I was wondering, why did Odo get sick from the Changeling illness last, when he was infected first?