I think LeBron is on the juice, there is some evidence that he was involved with the Anthony Bosch's steroid ring. But I think a hard worker could put on 29 lbs in three years. Also, LeBron has shown a lot of the side effects of steroids whereas Giannis does not. They do a lot of cardio in the NBA, and that bodes for a lean body not a musclebound one. Giannis is still lean, LeBroid is built like a truck and shot up there really quick after high school.
Given the league stance on PEDs why wouldn't players use them as they turned a blind eye for years.