“Ashes’ Will” – “A Sad Journey” [Campaign 2, Mission 2]

An interesting point, or perhaps a bug. The garrison in the yellow territory can only be unlocked after defeating Erathial in the dungeon. Otherwise, the cursor does not become active for combat when hovering over it. And another thing: it remains unclear why there is a mage standing near this garrison, who, when approached, gives a speech about someone. This is not reflected in the quest list, nor does it activate the garrison.
Arantir's progression according to my scheme in the illustration; perhaps someone guided him in other directions?