So did Ju Peter and Warcury, and they obviously weren't successful either. And honestly I'd argue that Imu should be angrier at Kizalu for not doing shit for half of the raid on Egghead, choosing to cry and wallow on the ship for the most part. At least Saturn tried till the very end.
As far as we know, Imu's decision to kill Saturn doesn't seem related to his lack of power.