That's what I've always heard - Sleep is broken.
Not really "broken", it works how it's supposed to, but the status itself is just bad.
For example, you can just let them hit you while using an Ironmight Plate set and the Slooms will deal little damage, but actually heal you with the status.
And Sloombargos could just keep you in place forever if you're soloing and end up in their mist. They'll just keep re-inflicting the sleep status over and over until you die.
It's just broken. I know many people (including me) would like to see them back in the Clockworks, but first a fix has to be made.