From what I understand slings had more "umpf" than people give them credit for. Good burn though.
Eh, it was mostly a joke, but they are still nowhere near in the same league.
It's considered a more primitive weapon for a reason.
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Slings if handled by a person who can use them are in the range of 80 to 180 Joules, that's quite of lot for a pre-gunpowder weapon. You can find such tests on Youtube for example. There is some very misleading data about slings, some think they are very weak (scientists trying them first time f.e., like in "From Sumer to Rome", stating less than 30 Joules energy), some call them the equivalent of an ancient gun (total nonsense). Anyway, properly used they are at the upper range of what stronger bows can reach. As energy is a result of speed (squared) and mass and many sling projectiles are of equal weight as heavier war arrows and bolts, it follows that they move at comparable speed.
The biggest disadvantage of slings is that they need a lot of training to hit something, much more than crossbows or even bows.
