If you're going to thirst, why keep beating on the trance'd assassin who can definitely handle the thirst? Why not switch to the (axe wielding) warrior and try to get some RNG love.
It's a money maker and kill sealing ability for sure, but I usually had to lead off with a curse/lucky damnation -svs to get the energy drain spam going. I'd say if the target had good svs I was only landing 1 out of 3 or so. I'm rather surprised that you're being troubled with -70 svs. Are any of the preps you're using cutting into your svs? Or did he land a lucky damnat