So, let me get this straight, you think that Darth Krayt couldn't defeat Marka Ragnos, but Dooku or Maul could?
Krayt used the Dark Transfer ability to save himself from the yorik coral seeds, which the force had no effect on. He fought off Abeloth, along with Luke, and his contribution, believe it or not, was actually greater. Krayt Reborn is one of the most powerful sith to ever live, as evidenced by his superiority over Darth Wyrrlock III, and pretty much every sith alive during the legacy era. And that was a time when the force had given way to the dark side to reign supreme.
As for Tulak Hord. We know that he could take on armies of jedi in his time, but then so could Exar Kun. And he wasn't as powerful as Plagueis, who was probably the most powerful up to his time, or as powerful as Caedus, who was said to be immediately stronger than Vader.
Yeah, he was treated as a throwaway character by those who created him, but he is meant to be this really powerful sith. Also, he survived for thousands of years at the center of all the turmoil on Moraband as one of the most prominent sith figures, so he technically does have one "thing he did" to his name.