Thief (WvW and PvP): Hidden Assassin Trait
100 power is usually <5% damage because these builds easily have >2000 power already (approaching 3000 in WvW or 3.5%).
Even if we were to be generous and use 5% the deadly arts build would still come out ahead—it gets 15% from traits while the shadow arts build has +10% from full might stacks. This only occurs for a short time after refuge or if they spend an inordinate amount of time setting up with black powder. Additionally they lose out on the +20% crit rate from fury on steal, or they lose out on 2k damage/poison from mug (which could easily account for 10% of the damage required to down a target).
Conclusion: the offensive power of deadly arts is still far ahead of shadow arts.
Every class has a GM minor trait that has something to do with damage, even the defensive trait lines