One Slayer is a combatant good enough to wreck good duelists that would give Outlander some problems.
Now, those good duelists were adjusted to fighting the Vong after years of war. With someone who fights an amphistaff for the first time, who faces Vong tactics the first time in his life, and has to suddenly fight without any reliance on Force Sense? Essentially fighting a being outside of any of their experience, training, without reliance on the Force Sensitive's biggest strength? A being that's also perfectly suited to fight the Jedi?
(As an aside, I think it’s important to note that Nox has fought without her senses or connection to the force in general as early as Act 1)
It’s hard to see anyone other than an absolute top tier force user (like Valkorion or Krayt ) defeating Outlander. Even if we assume that any average slayer > Kyp Durron, the Outlander has defeated and surpassed beings that either scale above or have caused the devastation and consumption of planets and solo’d hundreds, if not thousands upon thousands of Jedi and Sith.
And, although this isn’t important, I don’t see 3 slayers succeeding where the Dread Masters, Revan, Vaylin, the Machine Gods of Iokath, and Tenebrae failed.
__________________ ”You presume limits to my power. There are none.”
The main point here is that if even Kyp Durron, an insane powerhouse struggled with just one slayer then the Outander pretty much gets crushed with three here