I'm more of a moderate slinger myself, in regards to slings. Not that I have much weight in my opinions, being another novice.
I agree on some sources such as Xenophon on the ranges of slings (Which likely exceeds 400m), but I tend to disagree on the ancient sources relating to pin-point accuracy of slingers, such as was achievable by the Benjamites for example. You can certainly achieve good accuracy, but likely not further than ~20-50m.
In a battlefield context though, accuracy doesn't really matter all that much with virtually all projectile weapons except firearms, because when the engagement distance is going to be longer than 100m or 200m, you shouldn't really expect to be all that accurate or have that much of an effect militarily, excepting shots to exposed and relatively unarmoured parts. This 100m-200m range doesn't seem to change until at least the ~1850's, and by the 1900's, soldiers could expect to hit opponents 400-700 meters away.
This is why you want hundreds of archers, crossbowmen or slingers in your military forces, because ranged combat is a numbers game, and for every one-hundred or two-hundred arrows you launch, you might only get one or two enemy casualties.
I personally feel that Accuracy is more important for when the distance reaches within 50m or so, or more at the 'point-blank' spectrum, because at that distance it is more likely that you can actively aim for individual or grouped opponents and expect a hit. You can also use larger rocks in the sling!
This also counts for Archers and crossbowmen. Crecy and Agincourt were likely fought at closer ranges, for example, than is commonly thought, possibly within twenty meters. At this range and on the flanks, English longbowmen could easily hit the exposed maile-covered armpits, visor-slots/breaths or for the back portion of the legs, places where the plate's might not cover. This would not be possible from longer distances, as at a range of 100m or longer, the English arrows would likely be deflected or glance off of french armour, such as plate armour or coat-of-plates et cetera.
The benefit of the sling though, likely lies in the cheapness of the projectiles. So, in my opinion, it is possible that slingers likely had further engagement ranges than archers for a large period of time, even when it could be possible for slingers to be within the 'maximal range' of bowmen, likely because commanders didn't want their archers to waste their arrows et cetera, because that stuff costs money. Meanwhile, anyone can make clay balls and bake them, supposing they had clay. Lead is an even better, but more expensive solution as well.