Characters like Jiren and many other fighters from the Tournament of Power, the top brass of the Red Ribbon Army, and certain forms of Majin Buu could all be interpreted as leaving something to be desired.

Source: https://www.cbr.com/dragon-ball-super-gas-worst-villain/

Fortunately, Toei eventually ordered Dragon Ball Kai: The Final Chapters – a full adaptation of the Majin Buu arc.

Source: https://www.cbr.com/differences-same-dragon-ball-z-kai/

While this led to the evil in his heart being expelled and taking on a villainous form of its own, Majin Buu still came back to become a hero in his own right.

Source: https://gamerant.com/dragon-ball-super-every-main-characters-age-height-and-birthday/