But if there are no consequences why don't the Syndicate just take over? Clearly the Sultana can't stop them. Or punish them for anything they do. The Syndicate could apparently drug her, frame her allies for crimes, and do whatever the hell they want 24/7 without ever having to fear punishment.

If they cannot be held accountable for anything they do, why even bother keeping the Sultana in power? What is she gonna do if they attempt to kill her and take over? Cause what I have seen is if they did so, her only option would be to ask them nicely not to cause she lacks the power to do ANYTHING.