Just curious to see if the introduction of phys immunity removal via GC is now opening new weap options for merc ? (instead of reaper's)

do we just go botd or something else

Reapers is a good temp weapon. But it has cold damage, destroying a lot of bodies. If your merc does the killing, botd is the best by far.
You can erase phy inmunes using lacerator, killing then yourself using berserker, using gavel of pain amplify damage charges...

I use WW on my GF barb and he has zerk to two shot phys immunes. IMO it's not worth giving up EG charm spot for sunder.

I mean for war cry it's nice cause I can put botd on merc and gets more loots, also faster kills