I think this is the easiest and cleanest way to implement the cages.
Prevents having to kill off unwanted thralls.
Allows them to add crafters to be rescued from cages.
Could even rescue animal followers from cages.
Can even leave the unwanted thrall in the unlocked cage that someone else can loot until the cage resets.
I’m like you if the cages just offer a low tier fighter that I have to dispose of whats the point of bothering with it.