The Vengeance skill node Dark Duelist which gives 100% increased global damage is not increasing damage over time. While the display does show the 100% increased damage within the character menu the actual damage increase does not take effect.
I tested a naked character with 103% bleed chance using pure bleed idols with and without the dark duelist skill node. One set of test was done with single hits noting the first 2 ticks of the bleed damage over time after each swing. The other test used a series of swings clocked at 5 seconds each before monitoring the first 2 damage ticks. Both tests showed the same average bleed damage being done to the training dummy. Total testing time was over a period of about 10 minutes.