Valinhall vs. Elders and Estyr Six
Valinhall vs. the Great Elders is an interesting matchup because it depends entirely on which one they're fighting. Against Nakothi, for instance, a full team of Valinhall Travelers would do even better than the Emperor and the Regents did. They would tear Nakothi apart with minimal losses.
Same goes for Kthanikahr or Othaghor. The Emperor WISHES he had an elite team like the Valinhall Travelers when he was going after Othaghor, because he basically just spawns endless minions.
Against Tharlos, on the other hand, the Valinhall Travelers would just have their minds warped and go insane, or they would be turned into ooze or a lamppost or something. He breaks all the rules. Urg'naut's shadows would be able to kill Simon without him ever being able to resist, and Ach'magut would arrange matters so that it never came to a direct confrontation.
Versus Estyr Six...I guess it depends on how many Valinhall Travelers show up. All thirteen could definitely do it, six would be pushing it, three wouldn't be enough.