Darth Revan is the exception to the Sith rule, not Malak, Malak did exactly what most Sith do.
Malak was a barbarian who relied on strength rather than cunning.
Remember Revan was attempting to leave key infrastructure intact for once he would of taken control of the republic he could of quickly rebuilt the fleet and met the Emperor head on and actually could of waged a successful war against him.
All malak did was rip puppies heads off for the sake of craps and grins. Revan used the darkness to his advantage, Malak was simply consumed by it.