To be fair there are a lot of clues scattered around readable books, dialogue, and other events throughout New Kaineng City pointing to Purists hiding out in the edges of the old dead sector. Grub Lane is a hotbed of Purist activity and it's right there. It's a perfect spot for the leadership to hide out and a natural progression through the zone.
It's just that, when the player arrives, there's a mass of equally distributed undead, active Jade Brotherhood and Aetherblade camps, and no purists?