When Secrets of the Coven (Diaboloist) triggers and turns your Incinerate into Infernal Bolt, it loses its interaction with Fire and Brimstone which causes Incinerate to hit all enemies for 25% of its damage. It becomes a single target attack with ~3x the damage but only to a single target.
Feels like a nerf to me. It should continue doing 25% damage to surrounding enemies.