Darth Revan is the exception to the Sith rule, not Malak, Malak did exactly what most Sith do.
Revan an exception? No, just no. Plenty of sith who were like Revan. Bane, Vader, Exar Kun. Kun wouldn't of wiped out a population center like that to take out 1 jedi. That's simply overkill and frankly stupid.
Malak while strong, and he did have a few moments of brilliance, he was more of a child snapping the heads off of puppies.