In fact, Black Dragons are not prone to exposing their Inverse Scales willingly because protecting this scale is an instinctive behavior for them.
Even in death, a Black Dragon usually cannot unleash this powerful skill. It was only because Du You had taken control and intentionally exposed the Inverse Scale to meet the enemy's attack head-on. After being attacked, the Inverse Scale naturally enhanced its attributes, a skill most of the Dragon Clan do not possess.
Even those who have it rarely experience such a significant boost. Du You's Black Dragon happened to have this skill, and coupled with the enhancement effects of its passive skills, the results were particularly pronounced, which is why Du You used it deliberately.
Dark Devour is indeed very powerful, but it is more useful when clearing out large numbers of enemies. In one-on-one fights, especially against opponents stronger than oneself, being able to inflict any damage is already an achievement.