The Decaying Ghouls you are instructed to kill by General Summer are misnamed. The target is in fact the very same Venomous Ghouls Guard Seven, who initiated this quest, had you kill for the An Example quest
For Light Armor Classes and Heavy Armor Classes who got all the pieces of their Minister armor, even a charm should be unnecessary to deal with Yansheng, Hirudini Barbarian. The same goes for a Venomancer with a Crystal Magmite or better yet, a Glacial Walker; they are excellent tanks. A Mystic may be able to heal the Devil constantly, but should not count on it. Other Arcane Armor Classes will find this an extreme challenge, at the level at which it is offered
The reward, the Duke Weapon is sufficient to justify arranging a squad for