The Outpost documents make it clear the temple was founded with Jarrus and Morna. They arrived with settlers. So Moonhaven was founded at the same time. Jarrus is the one who led the clerics into the Underdark. During this, they encounter the Drow and the spectator which we know was summoned by Xargrim. They are the ones with the forge book stating Yali created Grim and guided the Sharrans in building the forge.
Dhourn makes it clear, no one knows where the forge is except him, and if his rivals are gone, you must die so that he can claim the forge. If Ketheric was around then, at the forge, or the Sharrans or Yali, that doesn't make sense at all. How could they claim the forge if it was founded and owned by Sharrans who were obviously in the area around that founding time.
