Darish Vol vs Arcann

Who wins and why

Vol wins imo. He fought Abeloth and severely injured her. He did it through a special technique but nothing says that it doesn't work on Arcann. Even if it doesn't, his performance is still good. He managed to block some attacks of Abeloth. We all know how powerful Abeloth is. She destroyed a city. Vol also had much of Luke's power. We don't know how much but it's still impressive. It's probably more than %50.

FYI:

Widely regarded as one of the greatest Sith sorcerers in the Empire, the enigmatic Lord Fulminiss is a master of the dark side's most arcane and lethal aspects. The grotesque Harrower assassins are his most famous creation, but legend has it he once summoned a raging storm of pure Force energy that disintegrated a rebellious city of natives in the Imperial-conquered Jabiim system.

Lord Fulminiss is a respected expert on the topic of mass extermination, and at the Emperor's request, he has performed extensive research into new ways of eliminating planetary populations. More than one Dark Council member has paid handsomely to obtain a record of Lord Fulminiss's work for his or her private perusal.

Taken from SWTOR: Codex Entry: Lord Fulminiss

Hero of Tython was able to defeat/kill Lord Fulminiss in single combat on Voss.

And it is established in SWTOR that no matter which class is taken to represent The Outlander, Arcann was much stronger than the protagonist.

Arcann, due to superiority to early Outlander and blocking Valklander's lightning

Arcann.

arcann

Vol's circumstantial feat doesn't impress me nearly as much a pre-prime Arcann stomping the Outlander in the Force and defending himself against an admittedly much weaker Valkorion's Force storm that could kill hundreds with the residual energies alone.