Below is the Top 5 bullpens according to fWAR. The "Total" is the total fWAR of relievers not including the "closer" and "setup man," which is essentially the entire bullpen aside from the top two fWAR numbers. The "Average" is the average fWAR of those relievers. The "Difference" is the difference in fWAR between the total of the"closer" and "setup man" and the total of the rest.
These are rough numbers meant for entertainment more than anything, but they can provide some sort of evidence of bullpen depth. Obviously, the higher the "Total," the deeper the pen. Also, note that I included all relief innings, meaning leverage and reliever role were not accounted for in the total.
This tells us what we already know: the Braves need right-handed relief. The difference in fWAR between Craig Kimbrel + Jonny Venters and the rest of the bullpen is enormous.
Something else that's not that surprising is the difference between the "closer" + "setup man" and the rest of the bullpen gets smaller as the bullpen fWAR gets smaller, as well as the total. The top two relievers in the higher-ranked pens have fWAR's that catapult their entire bullpens to the top of the list (Kimbrel/Venters, Rivera/Robertson). The better they are, the more they're used, the higher the potential fWAR.