I think arcing back turbolaser bolts, telepathically dominating scores of Jedi including Jacen, almost mentally dominating Luke, and ragdolling Luke are more impressive than one-shotting Darth Marr. Jacen thought that UnuThul was more powerful than Luke.
Originally posted by XSUPREMEXSKILLZ
1. I'd argue there's a clear difference in how each feat, (I.e. Nathema and Ziost) was carried out. In SWTOR, Vitiate was dormant until the Revanite War had allowed him to feed on enough of the victims of the conflict so that he could travel to Ziost. On Ziost, he does something similar: he mind controls the populace and as people die throughout the conflict, he feeds on them to become more powerful. If it was as simple as using the energy of the populace, he would have done it as soon as he was able to mind control the population. Rather, when enough death was caused from the conflict, he was able to consume enough energy to swamp Ziost in a tsunami of dark side energy, thus commiting genocide on the planet and consuming every last living thing, from the people to the Biota to (presumably) the atmosphere itself. This resulted in Valkorion, a man with the consumed energy of billions and one of the most powerful dark side nexuses in the galaxy coursing through him, along with his haxx as a spirit. It's no wonder he's oneshotted just about everyone he's come across, from Marr to Arcann to the Outlander. It's hard to tell Valkorion's upper limit due to the fact that he hasn't ever really been taxed when at full power, but I'd wager he has what it takes to handle Unu.
Ok, so he needed some threshold of energy to pull the feat off in the first place - this still doesn't counter the fact that he didn't pull it off under his own power, and certainly not in the timeframe of a combat.
2. That's fair, but hardly negates the point that Valkorion is too powerful to be ragdolled by really anyone bar The Ones.
Even if that were true, I'm not claiming UnuThul will dominate or ragdoll him, just that he'll win, given that he's heavily implied to possess more raw power than Luke.