We have this ol' WoJ gem which I believe can be applied:

Hmmm.  In terms of pure, raw power, several who have appeared or been mentioned in the books could pull it off, though neither side would really “win” as much as “continue to exist.”  Plus, the sudden absence of Mab would do freaking HIDEOUS things to the earth.  But here’s who has the necessary horsepower do it:

o   Titania–though it would be a coin toss.  Almost literally.
o   The Mothers (who wouldn’t)
o   The White Council.  As in, ALL the White Council.  Every wizard on the planet.  And they’d need her Name.
o   Drakul.
o   Ferrovax.
o   The Red Court–again, ALL the Red Court, though their odds wouldn’t be good.
o   The entire White Court–very, very long odds on that, but if they actually pulled it off, whoever took Mab would effectively control her power.
o   Cowl (if the Darkhallow had succeeded).
o   A union of the old Elders of the Black Court.  They were freaking scary until the Whites arranged to have them hounded down by mortals.

All of that, of course, assumes that Mab is standing there alone, outside of Faerie, and not commanding an entire nation, literally millions and millions and millions of nightmarish creatures of every description.  Which she does.

There’s a REASON that when Mab said, “Sign these Accords and abide by them,” people listened.

*****
Shift back... if it would take the entire White Court to overcome Mab, I can't see enraged Thomas taking on a Titan without significant assistance.  Now, you wouldn't need Thomas if you already had Alfred.  Unless somehow the Titan is weak to White Court power.  So can't see Thomas really helping there.

Yeah, while reading it, I totally assumed it was somehow a major sign of a geasa lifted or some type of time/power tweak, the fact that young, developing wizards got it and Harry was getting it then.  As silly as it is, I suspect it is actually rather significant. 

A worst case scenario would be Jim split the books and needed filler for the 1st one but that just does not strike me as Jim.  And I love the idea that it would enhance his understanding of summoning / creating via NN.

Reading all this got me thinking (related):

What if the betrayal involves Eb setting up Thomas for political purposes of the White Council?
It would fulfill several of these loose ends and cause one hell of a kerfuffle amongst all the parties.

Raw magical talent - yes.
Developed skill and strength - no.
Political acumen and connections - no and not exactly.

Harry is a brawler with raw magical muscle but lacking in finer control.
His repertoire is actually  sort of broad.  He would eventually make a great senior council member - in the future. 

But lets compare him to a few we know of:
/the definitively superior list/
The Merlin: Oh heck no.  The Merlin has done things on and off screen on the fly that suggest his strength is at least equal and the talent gap is wide.  His connections and acumen eclipse Harry's despite Harry being Winter Knight.
Eb:  Vadderung has stated Eb would mop the floor with him.  I agree.  Harry is inferior in every way.
The Gatekeeper:  Same.

/the most probably superior list/
Martha Liberty: The White Council's Spymaster.  Obviously hyperconnected. Pulls off a veil that gets past Harry.  Otherwise, limited knowledge but has Eb's respect.
Listens to Wind:  Defeats Shagnasty, albeit with an advantage for him.  Does things that make Harry go wow. 
Ancient Mai:  Not a combat wizard but the White Council's "magical engineering/artificer expert".  Heavily connected.  Everyone seems to kowtow to her so I presume she is nothing to sneeze at.


Cristos: We know nothing here but we know he is heavily connected.

Harry's one advantage I'm ignoring is Demonreach but I don't think that's a usable power-up or device.

If Harry were put on the Senior Council, it would be for morale or political consideration (to ally the Winter Court, for example).  I'd like to see it but on a raw level he isnt ready.

I don't recall... did we know before this that Connie is

(click to show/hide)

Lara's daughter?

That'd make her Thomas' niece, too...
 

I think you're misreading that line.  She is referring to being in Lara's territory, not her Father's.  She isn't going to refer to her Father as "Count Barrrowill" or whatever.

Confirmed two books.

Ordered ... because Jim.