That fine, except a perfect rationalist doesn't exist in a bubble, nor does Harry. Much of what's making the story feel rushed isn't Harry's actions, but rather the speed at which those actions propagate among people who are not rational actors.

Harry is not an above-human-intelligence AI with direct access to his source code. Therefore he cannot "FOOM", therefore he's stuck with a world that is still largely outside his ability to control, no matter how rational he is.