There is a good reason I use Rostam(A) for Dynamis[D] fodder and general farming in other content: Welcome to my regional COMCAST bottleneck broadband.
For me, in mixed ranged and melee situations, Rostam(A) is best. I'm not going to swap back and forth between A and B when dealing with fodder and minor wave1 and 2 NMs. The TP loss swapping weapons needlessly is silly. Also, the lag in Dynamis coupled with an often bottlenecked bandwidth internet service makes engaging fodder mobs and statues immensely taxing. For most part, I end-up shooting fodder and meleeing the minor NMs.
(One of these days, another broadband will move into my area and replace Comcast...and maybe I will optimize my playstyle to a more responsive internet connection.)
However, in situations where I am 100% meleeing NMs like Wave3 bosses and certain Master Trials, Rostam(B) pulls ahead in both Tri and Quad gearsets. My Tri set happens to have a bit more acc if I need more acc when support is not optimal. Should I need to swap into Malignance DT set, Rostam(B) still gives me a 2-4 hit round.
When support is optimal, Rostam(B) pulls ahead superbly in my Quad gearset. I tend to hit an average of 5x per round. The range per round is actually 2-8, but I rarely hit 2 per round. The TP gain is something like 1-2k per second when gear swaps correctly. I'll get an extra 20-something more Leaden Salutes on a 10-15 minute Wave3 boss kill than other top tier CORs despite my incredibly bottlenecked internet service. 25 extra 50k-90k Leaden Salutes means I pull ahead in parse by 1-2 mil dependent on support optimization.