He was probably more interesting before he went Dark. He's has brute strength, and is a wicked fighter, but something of an idiot. His tactical sense appears to go no further than "take club; smash obstacle."
Take Telos for example. The place was a potential hiding spot for Jedi, was crawling with failed apprentices and their FS descendants, had some impressive military structures, and was on a moderately-traveled Outer Rim hyperspace run.
Revan? Okay, plant a handful of spies among the Agri-Corps and send some "recruiters" to sniff out anyone else with ernough anger and Force potential to be useful. Then, stratigically hit the cities, send HK-47 to nail the local government, and activate that fifth column you've put in place to convince the locals that signing on is a good idea.
Malak? Bomb planet to ash. No military salvage, no infrastructure. No Dark Jedi recruits. Just a useless ball of poison rock. Total waste. Worse, the Republic has an atrocity to rally around and inspire their troops. Malak proves he's good for brute force, but that's the ONLY thing that guy can do. He's good as an enforcer, but as the one who will carry out the Big Plan? Not so much.
I'm betting Revan was at least shopping for a second apprentice, if not already training one (see the most excellent Brotherhood of Shadow mod...Matilda would be an excellent choice), and Malak's attack on Revan's ship was part to usurp the titla, but primarily to save his hide.