Maenads are worth their cost in food. They tend to stay to the death when berserk.
They won't be your only unit, but having a mob of them to deal with in addition to other forces, makes them effective.
Same observation for Ulm vs. Maenads. Put shortbows behind the infantry of Ulm block, and the bows can take care of the maenads and let the infantry hold up longer.
As for the comments on slingers... I would like to see the sources which claim they are just as effective as shortbows. Maybe nearly as good, but I think they would rate somewhat lower damage, range, and accuracy than shortbows. There may be some factors to favor slingers (lighter, cheaper equipment), and yes they might supplant their ammo with rocks more readily than archers might replenish their arrows. However, military slingers would I think generally use sling bullets rather than just any rock. I don't think they had a better rate of fire than archers in general. I'm also extremely suspicious of the claim that a sling shot hitting a shield was likely to have a very useful effect.
PvK