It is not the only Dark Sun weapon that is pretty sweet. Getting brutal 2 on an axe with no Superior Weapon Feat is pretty good.
But there are a lot of weapons even in the PHB that are clearly superior to other weapons, either due to simple stats or the feat support behind it.
Try being a master of the flail if you don't believe me. It is not pretty.
My games are wide open, and not only does no one use a sling, no one also uses a dejada.
So, y'know, better or not, it still kinda sucks.
Don't you need a free hand to load the sling?