Well, I wouldn't say that they're immune to Dhar, a Doombolt will blow them up and incinerate them just fine.
They're just highly resistant to magic, not immune to it.
I'd say that sorceresses are liable to just have regular human slaves, rather than halflings. There's a far greater abundance to the former compared to the latter across the world in general. Like, halflings get around, certainly, there are a few amongst humans in most places of the Old World save perhaps Araby, but still.
It's said that they can certainly handle magical objects and the like with far greater ease and lack of concern than most others, even dark magic related ones, yes, but having one around would likely require a lot more customized equipment and tools made especially for them whereas a human slave can be about nominal in exchange. I'm not saying that it wouldn't or couldn't happen, just that I've seen very little evidence for it. Additionally, they might well be more difficult to discipline and keep control of specifically because of magical resistance, whereas certain magical efforts to contain and bind humans would be easier.
They're just highly resistant to magic, not immune to it.
I'd say that sorceresses are liable to just have regular human slaves, rather than halflings. There's a far greater abundance to the former compared to the latter across the world in general. Like, halflings get around, certainly, there are a few amongst humans in most places of the Old World save perhaps Araby, but still.
It's said that they can certainly handle magical objects and the like with far greater ease and lack of concern than most others, even dark magic related ones, yes, but having one around would likely require a lot more customized equipment and tools made especially for them whereas a human slave can be about nominal in exchange. I'm not saying that it wouldn't or couldn't happen, just that I've seen very little evidence for it. Additionally, they might well be more difficult to discipline and keep control of specifically because of magical resistance, whereas certain magical efforts to contain and bind humans would be easier.