3d6

Goblin Genie Warlock X / Twilight Cleric 2, using Twilight Sanctuary to force dim light onto your target, thereby gaining advantage on your Shadowblade attacks. Take your first level of cleric early to get heavy armor proficiency, but save the 2nd level until after you have Shadowblade available. Genie adds a PB damage rider of your choice of type of damage--Dao may be an interesting play b/c you very much could play this as a Str-based warlock, and pick up Crusher (Str) to even out Str and combo with your allies' AoEs. Starting stats with point buy could be 15+2 10 14 9 13 13+1. Make sure to take Eldritch Mind as one of your invocations. Goblin affords you another PB damage rider for PB turns per day, to help make you feel a bit more like a rogue with your damage output.

If you want to be ranged, you could throw-and-recreate your Shadowblade every turn, but that is IMO pretty inefficient and feels really bad if you miss. In melee range you could instead be hitting twice with a light Pact weapon, and then once with the Shadowblade with your BA. Handaxe, Scimitar, and Shortsword all have a d6 damage die, so are good candidates. If you decide to get Dual Weilder feat, this build would work really well with a versatile weapon (Battleaxe, Longsword, or Warhammer) so that if you don't have Shadowblade up for whatever reason, you are doing better damage with your pact weapon. You lose the +1 AC in that case though.