The cool down of 9 seconds hardly matters as by the time you are ready to do a second one the 15seconds of FiB has elapsed and you can do that instead. especially as you HAVE to have WM on it for the crit and the good damage that makes it's a 10.5 cooldown,. It has a 1.8 second cast with level 50 alacrity modded gear, 2 seconds un-modded. oh look that's got you 12.3 seconds after the cast time. For 1/3 the damage / the same damage, with 3times the work. That 50% gets you to a stimmed out 4100-5kish(due to it's much lower starting damage).. and a stimmed out FiB will give you 3300 - 4400 depending on spec.
And I guarantee you the crits on FiB on running right around 38% for most people so using the Potency will give you the guaranteed crits you need as well.
Remember to give the crit, it's WM (instant 1.5 seconds GC)Fight begins, Turbulence (1.8-2.0seconds.) 1.5 GC, wait 9(you aren't you're casting other things), you Have to have the second one off in under 1.5 seconds without moving but you are already to to 13seconds. And in 2 seconds you have FiB again. And look the waiting on the Global cool down you did to assure the setup on Turbulence makes that more realistically a 15second cool down.
The point being that for a 31 point talent it's sorely lacking.