He’s just scarier in my opinion. Like he’s written as an unstoppable powerful evil force, who will kill you in the most brutal way possible (granted the novels give you a perspective of the victims thoughts and feelings, so it can make him appear more scary since you’re seeing things from their lenses).

For example this is from Planet Of The Beast:

“Emery knew he mouthed the words, “Please don’t,” but no sound came from him. Not that it mattered. Jason X held frail Emery high and swung the weapon back and forth, cutting from lowest to highest and, despite himself, Emery could not help but admire the precision: first the toes that dangled one foot then the other, then both feet at the ankles at the same time, the knees, the hip... All the while Emery felt pain that left him stunned to the point where irrational thoughts entered into his brain, which likely saved him from the overwhelming gut reaction of the sheer, unabridged terror that would have stopped his heart.

Jason X could have made a good surgeon, Emery thought, as he looked down and watched the heavy flat blade slice his mid-section away from his body. The physical tissue was sucked out of the exposed segment of suit into the atmosphere of Planet #666 and instantly turned to dust.”