When Shazam becomes a dark and twisted version of himself in Year of the Villain and fully unleashes against the beloved villain Black Adam, it shows that the young hero has always possessed the power to take down his greatest foe. However, even though Shazam has the power to kill Black Adam, he chooses not to. The reason for this could be that Black Adam is not truly evil, as he proves in this story when he relies on the power of his words to teach the young hero a lesson.
In Black Adam: Year of the Villain by Paul Jenkins and Inaki Miranda, Black Adam is met with doubt from his advisors about his ability to lead the nation of Kahndaq. While addressing their concerns, an erratic Shazam — who has been twisted and turned evil by the Batman Who Laughs — appears in Kahndaq, flaunting his excessive powers and declaring his intention to depose Black Adam from his position as the country's ruler. Although Black Adam can fight and beat notable heroes, the Kahndaq ruler mostly tries to let his words do the trick, imploring Billy Batson to see that he is not being himself.
While Black Adam tries to get the altered young hero to see reason, Shazam ultimately wins in a physical fight. Even with the armies of Kahndaq firing upon him, Shazam still smacks Black Adam around until the ruler lies in the sand, utterly defeated. Rather than finishing him off, he gloats over Black Adam's beaten body, pointing out how he is stronger and faster than his longtime enemy. Once the sun comes up, the people of Kahndaq are able to use the power of their prayers to summon a lightning strike that traps Shazam and turns him back into Billy. Black Adam then lets him leave with his tail between his legs, warning him not to come back.
Black Adam has a history of being the villain in Shazam's world, but this role reversal allows readers to see a different, less evil side of him. By not defeating Shazam physically, he appears more human as he urges his citizens to avoid violence and lead by example. Black Adam also understands that even though Shazam's abilities are vast, with him taking down both Batman and Superman, beneath the hero-turned-villain is a kid who is not used to possessing a significant amount of power. Adam chooses this battle carefully as he can see right through Billy for the child that he is.
His one-man invasion of Kahndaq and beat-down of his enemy prove that Shazam's powers grant him the ability to get what he wants. If he were to every fully unleash himself again, it would be too much for Black Adam to handle. The fact that he has not done this shows that Billy chooses restraint in his usual encounters with Black Adam. This could have to do with the change in demeanor and perspective Adam displays at the end of the story. He recognizes that he has underestimated the power of his people, and the manner in which he defeats the villainous Shazam shows that underneath he is a decent person. Black Adam and Shazam both experience new versions of themselves in Year of the Villain, and in a way it ends up being an unexpected yet refreshing victory for both characters.