Elegast,
I'm with you on nearly every piece of this, but I had a different take on the Blackstaff.
My mind took:
MW's missing walking stick,
WOJ on the Blackstaff preventing insanity,
Outsiders/Nemesis' tendency to cause insanity,
Winter's current purpose (defending against Outsiders), and
[I forgot who]'s theory that the Laws of Magic exist to prevent Outsiders from gaining influence...
...and cooked up the FrankenWAGTM that the Blackstaff is specifically a defense against Outsiders' ability to exploit openings made by violations of the Laws of Magic (among other things).
That's... a really great idea! And it made me realize something that should have been obvious: if Knnn's
theory that that the Laws of Magic exist to prevent
Outsiders from gaining influence, then Harry, who has a special immunity to Outsider mental attacks, may be able to violate the Laws without becoming mad! A living Blackstaff!
If this is the case, I doubt anyone on the WC knows MW's walking stick's true purpose (i.e. allowing Death itself to walk freely among the Outsiders without being vulnerable to their corruption), save maybe for Rashid. If Rashid had ever confronted Eb about returning the Blackstaff, that could explain the apparent breakdown in trust between them that Eb refers to in PG*.
Possible, but I don't think so: Rashid was already alive (he took down the mad Arab around 700 AD) when the WC stole the Blackstaff (1065 AD). He could have objected far sooner. I think that the Gatekeeper suspected Eb to be infected when he came up with his grey council conspiration. In TC he clearly thinks that Harry may be infected, and he uses his eye to check. Eb knows about Rashid's suspicions, that why he asks Harry if the Gatekeeper is on their side.
*Also, in a rare double-whammy post, I don't believe that Eb created the Grey Council sometime between PG and TC in response to his conversation with Harry at the end of PG, as others have posted elsewhere. At the very beginning of PG, Eb tells Harry he's already begun organizing a group of people he trusts- I think the GC predates Harry telling Eb about the BC theory.
Ah. I had never thought of it, but you're probably right. It was used as a way to justify Mab's actions in PG, now that we know Molly's fate it's no longer necessary.
Lastly, if Mother Winter is Death, does that make Mother Summer Taxes?