It's a bit normal that it does higher damage if you add an ability in the rotation...
The 31pts-spec uses 5 hitters (2x Voltaic, Shock, Discharge, Maul) while the 27pts-spec uses 6 (the same 3 Force powers plus 2 Thrash plus Death Field).
If you want to compare properly, add a third Voltaic Slash at the end of the 31pts-spec's rotation (or Low Slash if in need to stop a guy and find a position for Maul or to interrupt him), so that both takes the same time to use (and note that if it's Voltaic slash, it means that while the 27pts-spec ends its burst, the 31pts-spec is already starting to build its next one).
I also hope for you that your Death Field hits only one person, or it will be hard to crit your Discharge/Shock.
I actually added the 2x thrashes in for the purpose of putting in the same number of hits as 31pts, but miscounted haha. Thanks for pointing that out. The 2x thrashes are only to lower the cost of shock, if you have lots of force (AKA just entering combat, and have Dark Embrace up) then you do not even need them. The rotation turns into Recklessness> DF> Discharge> Shock> Maul. You find me a 31pts build that does that much damage in 4 moves. That's why I prefer 27pts over 31pts. I do not need to use 2 thrashes/ VS to get my highest damage. No setup required.
I also am not having a real issue with hitting multiple people with DF accidentally. It comes naturally to me to aim it off to the side so that only my intended target gets hit. Does not always happen of course, but mistakes/ unavoidable multi-hits are infrequent enough that I can live with it. If I've got Recklessness up, I'm typically going healer hunting, and a smart healer does not stand in the middle of it all. And for those 75 seconds in between Recklessness, the AoE is always a positive.
I do still very much enjoy playing Deception, I'm just trying to point out to the OP why I prefer to not take VS, which was the original question he asked.
Side note: Does Overcharge Saber increase the damage done by Discharge? I've never thought so, but people keep seeming to throw it in before popping Discharge.