To be honest I don’t know if this would be better as a bug report, but I swear I remember these used to use both Smelters and Cooks, and now they use only Smelters. This seems more an intentional change I don’t agree with, than a bug. So in Feedback it goes.
I got a T4 Cook, completed the Master Chef journey, and now my new Charcoal Kiln placed in my kitchen is worse than the improved campfire I already had, since it has no thrall benefit (I have no smelter). It’s from the Master Chef journey, and the description on the hover text of the reward menu says it’s a kiln used for “smelting and cooking.”
But even though it can cook, it’s only good at smelting, because my cook can’t use it, and I have no smelter. When I get a smelter thrall, presumably they’ll wander confusedly between my kitchen and their furnace area.
It looks like a stone oven. I assume it was meant to be that more that than a kiln for smelting, because it’s from the Master Chef journey. But it can still do both, just the thrall it uses seems wrong.
If it can only use one type of thrall, it should only benefit from a Cook thrall and not a Smelter thrall, as fits the journey that rewards it.