What's the dungeon meta build?
I think something like this is the standard thief build. At least for a coordinated group. Ascended equipment is not required.
FA
5/6/0/0/3
Mug, Sundering strike.
Furious Retaliation/signet might, flank crit/more HP/signet mastery, executioner
Thrill of the crime.
All zerk. Utilities are the precision signet, breakstun/power signet, and depending on the situation smoke screen.
I personally still like this “classic” DPS build over the 6/6/0/0/2 as Revealed Training only very marginalize increase your DPS and mostly via using D/D Cloak and Dagger rotation on a single target.
SBI – Thief and the occasional Guardian & Warrior.
Haste is pretty much interchangeable with Roll for Initiative or Shadowstep. There are probably better weapon sigil combinations out there too, but that’s what I use.