I am quite sure I am the Duke of Dementia as I can summon dark seducers but during the quest "The helpless army", A golden saint messenger asks me to assist at Brellache and I'm quite sure I'm supposed to get sent to Pinnacle rock. Any help would be greatly appreciated.

re-read the dialogue when the Golden Saint Messenger talks to you. Either at the palace or at the fortress. You are supposed to go help them, and no, it isn't a normal occurence.

Oh I see thank you very much, I was unaware that if I was the duke of dementia I was supposed to help the Golden Saints. Thanks again

Retaking the Fringe and The Helpless Army are a pair. You assist one group in the first and the opposite group in the other. Also, you're supposed to end up being able to summon both Saints and Seducers, so you need to justify that with actions for both. It all builds towards your ultimate role at the end of the SI main quest.