You almost never have the twilight to use the Shaman in FBlock. If you're worried about
Greenleaf and/or
PATHS you are playing the deck wrong. You don't waste minions that will die to
Greenleaf,
PATHS, etc unless you have the appropriate counters (
isengard warrior, snows). Between
Sting and
Goblin Man you should have a very good idea if your opponent has
PATHS,
Secret Sentinels, etc and build your hand accordingly. Also, Shaman can't protect your non-isengard minions from
PATHS anyway, and it's not often that your swarm is 100% isengard. I can count the number of times I used Shaman's game text in the 100 games above on 1 hand.
The strength 6 versus 5 is also much better. If you can play all strength 6 or higher guys then they autokill
Merry FtS and it only takes 2 minions to overwhelm Frodo with
Sting instead of 3 strength 5 minions. If
Goblin Man wasn't discarded underground I'd consider switching to 4 of him and no shaman at all.