I'm not saying he was the most powerful of the four, i seriously doubt that. Still he was burried near the three others and he did create a blade. He did become one of the first Dark Jedi who apparantly all turned on each other, and yet somehow Ajunta still survived, and was later on burried in that particulair tomb.
So somebody must have thought highly on him, to place him in such a location. I'm just wondering if anybody has anything specific. Because putting all these things together just makes me think he was powerful, but I have no idea how powerful. Besides those other three there, those guys were extremly powerful. That he is not like them is no real surprise to me.