wasn't aware anyone said staff slings were less accurate.
As with most apocryphal slinging stories, probably someone who'd never used one.
A short handled staff sling is actually a lot more accurate than a plain sling as it's a much easier motion to repeat.
Also, while you can't aim it per-se - you can use the staff to point at the target.
As kick says, becasue you lack a windup on a staff sling you won't get more distance. But you should get more consistent results.