I don't get the point of the key if it were created by Azem too. In the large scope of things, what would be the final goal for them to have that key? Because from my remembering of what we heard of Azem, they are more of a "problem-solver" more than a big planner.
Besides, Azem presumably knew they would be sundered and thus lose memory of their Ancient identity. What would be the point of creating the key if there was no guarantee one of their sundered identity would find it, know how to use it and have the same mindset than the original Azem? Because as far as we know, sundered people from an original ancient can have very distinct endgames (see Ardbert and the WoL for instance, there was a time when we were almost enemies).

And while I'm not as categoric as Cleretic on Azem being a dead-end writing-wise, I agree that the more time people connect with their WoL, the less they will like anything added to the original Azem.I personally prefer the original Azem dead and gone, and the player evolving in the scraps of this history the way they want.