BH, I get a strange feeling of deja vu, as we've already had a similar debate on w6 (with alphabonkers and others).
I think there is no ideal tribal structure. In any scenario, you fit the structure to the available personnel. Any tribe that has BH in it can safely assign him duke and count on him to lead the tribe well. But not all tribes have that luxury, so they use different structures :icon_wink:
I have had good experiences with having multiple dukes. I understand what you say about taking power from the regular members by having a council, but the real reason for using a council is two-fold:
1) in advanced stages of a world, you become vulnerable to inactivity. Having a larger group of people sort of in the know helps fight that.
2) it reduces the strain on the duke. I can safely delegate the responsibility for an entire zone to one of my co-dukes.