It's definitely not fluff damage, and it's a very powerful spec, but it's a much harder spec to play effectively. Your major burst is going to happen around 5-6 GCD's in, if the dots haven't been cleansed already. Survivability is fairly low and lethality is out in the open most of the time with 2 fairly weak defense cd's. The lack of mobility.
until you start chaining culls with 2 dots on target, it's fluff damage.
if you can't get more than 1 dot on your target., cull is like shiv, but more expensive.
if your target dies right after you acid grenade them or otherwise goes out of range(or cleanses). you're **** until acid cd is back.
in a perfect scenario though the damage is pretty good, which is most 1v1's.
it's a real shame your flashbang doesn't cleanse your own dots.