[licker]

Yes slingers are a bit difficult to use, and some would say not worth their cost in the first place.

However...

If you play the standard theme (not Miasma, DT doesn't get slingers does it?) then realize that your sacred water dancers are 100% immune, and if you go for the right blessings (9water is my fav along with some fire) you can have a decent army of slingers and dancers. Try to add in some undead for fodder or for other purposes or use the drakes bog beasts and other 100% immune summons to add bulk or power or whatever you miss.

Though I usually find myself only using slingers in smaller armies or raiding Groups with small amounts of undead or constructs, I don't think they are particularly viable (on a cost basis) for your main army, though a small group of them placed properly could help, but as things degrade in the heat of battle you will wind up with your 50% troops getting poisoned.