The DK Ardent Flame passive Searing Heat increases the duration of three abilities by 2 seconds. Two of these abilities apply DoTs. Obviously, if you increase the length of a DoT, you lower its DPS.
Two points into Searing Heat also increases the damage of these abilities by 3%, but that is a very small amount compared to the 25% increase in duration, which for a DoT is 25% less DPS.
Furthermore, a morph of one of these abilities (Searing Strike -> Burning Embers) causes the ability to heal you when the effect ends. But this passive increases the duration. All of this seems very counter-intuitive.
I realize this is probably small potatoes as far as fixing class skills are concerned, but it bothers me none the less.