I think that FS has a deep enough bench at this point that that is not necessarily true. I do think you should almost certainly be running Tide Masters, 2 Hippos, Backfire, and Drown though. But the other three, while very good, are not required.
I think Poison Elemental is well worth a slot, but different strokes for different folks. I saw Taylor running a Salaman Soldier in his meta deck, probably for the cheap Warrior Foe.