I do like pb more because of the speed. For range I use other weapons on switch according to situation. But, I have a nack for up-and-close encounters.
For those immune to poison/physical I think the -2x poison res on Grief isn't enough to break immunities to make poison charms perfectly usable. And it seems the physical immunes won't take poison dmg. since the weapon isn't "working" on them.
So, the best strategy (at least for PvP) would be to get i.e. a Monarch shield with four 5/5 Rainbow Facet's (poison) and a Death's Web to lower resistances by a fair amount on switch (W). Note: this is only usable for Rabies unless you make Death's Web your primary weapon (bad idea!).
For pure Fury I'd try out that Famine on phys.immunes and see if that does the trick.
And again, I advise you to wait on second opinions. I'm no expert.
Hope this helps.