With the 4th Superior Rune of the Afflicted equipped, none of my Ranger skills which apply poison have their skill facts updated to show an increase in duration. So I thought that maybe it was just a bug of just the skill facts not being updated so I tested it out in the Heart of the Mists and the actual poison duration matches that shown in the skill facts. There is no actual increase in poison duration.
Aegan – Human Ranger (80)
Leader of the Guardians of Light (GoL)