CoC alone probably isn't enough to defeat Imu, that's why he kidnapped 5 kings. He also didn't seems to have a DF at that time. He thought gathering strong people and having a bigger group in traditional way will defeat Imu but he was wrong about it. A little naive, but Teach took the different approaches. It's like every failure is a failed Iteration of plan and Teach's plan is the right iteration that will succeed.