To say that God is perfect BY DEFINITION is to say something not about a god but about its definer.
I have recently bought a translation of the original text of the Bhagavadgita, also known as "the song of the celestial one". I would encourage everyone who wishes to understand what it means that god is perfect to read the Gita.
In it the supreme god is referred to as Krishna, and the text itself is a dialogue between Krishna and the human prince Arjuna. It takes place on a large battlefield, right before the battle is about to begin. Arjuna is gripped by reluctance to fight since he knows that to win the battle he will have to kill his kin. Krishna tells him to pick up the bow and arrows he has thrown to the ground, and to not be afraid of what he has to do. And from there it gets really interesting.