I tested 2 blasters , lvl 24 and 35, in some regular solo missions and found defiance to be useless. I have geared my play to keep my health in the green and avoid the "defiance" situations. I use Stealth and Invisibility to set up best case scenarios for my solo missions and stay ranged in a team situation. Defiance needs an overhaul as suggested before this post before I will consider it a "boost" for Blasters.
Pinnacle
MaxEnergee lvl 35 eng/eng Blaster