He's not, though, he's actually just more powerful than people think he is. The guy collapsed a 270x90 ft dome with a Force Scream, and completely overpowered one of the top duelists in the mythos.
And in The Third Lesson, after Satele Shan dropped a cliff on him and he received wounds he would never recover from, Malgus fights two Jedi. One of them collapses two buildings on top of him, which Malgus held up before blasting away. He then pwns that Jedi by blasting through his lightsaber defense with lightning and burning holes in his body. This is Malgus before he vastly increased his power in Deceived. A good 15 years before the game.
Malgus was pwning guys who collapse buildings before he recieved a huge amp and gained 15 years of growth. And he did it while grievously wounded. Anakin is still getting stomped here.