I dont really think Halsin was even once adressed, called, or even mentioned as Archdruid ... Unless i forgot something, all NPCs i recall called him "first druid" ...
And while i believe there are many Druid circles where being strong = become leader ... until someone stronger appear. I think is perfectly possible that other Druids followed Halsin bcs he was simply old and wise enough.
Their circle is pretty scuffed yeah, got a hag and shadow druids operating freely in their house
