I still don't get all the Vaylin hype. All we know is that Valkorion finds her somewhat frightening, she can perform solid TK feats from vast distances, and she can choke a group of unsuspecting force users. Granted, those things are impressive, but don't really strike me as things outside of Caedus's ability to deal with. Honestly, she'd have to be even more powerful than Luke for him to lose to such a comparatively inept warrior.
Well, her resistance of BRAIN was immensely impressive, given the run-off bolts from one of the streams of lightning were instantaneously disintegrating people. After being unchained, she then completely annihilates BRAIN. With a thought. From orbit. Her power while being assaulted by BRAIN was causing shockwaves across the entire prison, overwhelming the Outlander, (and even Spirit!Valkorion, thouh he was weakened on Nathema,) driving creatures and their keepers insane, etc.
There's also her tearing apart ships for the keks pre-KOTET Chapter 1, her various TK feats throughout KOTFE, Chained Vaylin defeating the Outlander in KOTET Chapter 3, etc. NewGuy also mentioned that Vaylin was an inept warrior, but from what I saw, she was pretty much matching Arcann in sabers in KOTET Chapter 6, (i.e. she was still Chained).
If you scale from earlier iterations of the protags and Arcann, she's absurdly kek'ing powerful.
"I was lying! See? There's an Omniverse in the box. And that Omniverse died. But alot of the lives in it carried onto the new one. New broom--same handle."