There is no fun in having thralls and standing there and watching them complete the game in the current balance of things.
Without thralls Conan turns into actual survival game. Also some dungeons are undoable without friends, which is nice as it encourages people to play together.
They created these skulls over each boss to show how many people are needed to defeat it - a joke currently.
Anyway FC forgot that we might have a thrall limit on a server and we are stuck with this challenge until it resets.