Why wouldn't you use it? Knockdown, TA and poison ticks... just too good to pass up tbh, even if the damage is somewhat random at times.

But, but, but... didn't they increase the damage to Back Blast...? My current opening I use is along these lines (Flechette Round) Shoot First->Sabo Charge->Blaster Whip->(Flechette Round)Back Blast->Sucker Punch->Sucker Punch->(Sucker Punch). I'm not finding that I do any less damage, and I'm finding that I still do the damage I was doing previously. The main change I'm doing now is that I'm trying not to stack the Flechette Round ticks as much, and having the longer duration is helping with my damage. With the change to the Back Blast CD, I just need to incorporate a couple extra Quick Shots or "Auto-Attacks". I do miss the free Back Blasts, but I just can't see the major problem (in PvP) with increased Back Blast cooldown. No biggie for me at the end to be honest.

In places that warrant it, you could try Line of Sight pulling. CC a mob, with Corso set as passive, then pull another. Run around the corner so that they follow, tank and spank as needed.