You wouldn't hide the fact that you wiped out your enemy, that you were at war with, with your secret strike force. You use a secret covert ops organisation to gather intelligence and kill rivals that you're technically allied with, not to fight a declared war and then give credit to your political rivals.

The Merlin is portrayed as a bone-deep political creature. The idea that he would both fail to take credit, and allow a political loose cannon ne'er do well benefit violates who he is as a character.

There is a reason everyone knew about Seal Team 6 the moment Osama Bin Laden got killed.

Are you sure he wasn't?

The Merlin told Harry that he (the Merlin) and a bunch of the most powerful WC members were preparing a counterstrike, to end the Red Court permanently.

Eb told Harry to come to the meeting to meet the rest of the gang preparing for a counterstrike to end the Red Court permanently.

Later, Eb and Vadderung and a bunch of unidentified powerful spellcasters show up and launch that "counterstrike" in response to Harry's information.

It seems very, very likely that the Merlin's overwhelming counterstrike plans and Eb's overwhelming counterstrike plans are one and the same. It would be really odd if the Merlin were planning that strike without including Eb, and they'd otherwise be drawing on a bunch of the same wizards like Rashid and Luccio and getting in each other's way.

Heck, Eb's opening line is: "The Merlin is preparing his counterstrike, and we're trying to find out how much they already know about it."

And when Harry doesn't show up for the meeting -- because he's unconscious with a broken back -- Eb says: "There are people in the Grey Council who think you aren't to be trusted. They're very, very wary of you."

That seems like a pretty clear reference to the Merlin.

I can't imagine why you think that. The Merlin is a conservative, and very strongly opposed to division in the WC. The existence of the GC is a threat to his power and the unity of the WC. If he was aware of it, he would immediately denounce it as a conspiracy against him. Also, if the Merlin sanctioned the strike, there would be no need to use the GC at all, or to wear the hoods upon arrival.

They could simply have shown up as the WC with as many wardens as they could rustle up, plus their allies. The Merlin could have easily claimed credit for the entire venture to secure his political power, and to bolster the WCs power and influence.

I'm rereading Summer Knight, and two things really stuck out to me.

-Lea was under the influence of the athame when she sold Harry's debt to Mab.

-Mab considered Harry's debt to Lea—at the time of Summer Knight!—to be of equal value to Morgana's Athame, which Lea says has similar value as a Sword, not because of what it is, but because of who's it is.

At this time, Harry is not anything particularly special, beyond the fact that he has a debt. It sounds like, though, lots of wizards occasionally indebt themselves to the Sidhe, though few probably do so to someone on Lea's level. Why would Mab allow Lea to keep the Athame in exchange for Harry's debt?

And... I'd love to know how the Merlin told the tale of Chichen Itza. Did Harry get credit? Was he known to be dead when the final story was being told, so he was a martyr? Or was it all about members of the Senior Council leading a daring raid on the Red Court's stronghold?

The Merlin was not at Chichen Itza. It was the Grey Council, headed by Eb or Vadderung. They were not under orders from the WC, and were acting on their own initiative. The Merlin would not have told any tale. Instead, he would have simply listened to confused news reports, and inferred what he could from what he knew. The wizards who participated would not have told anyone who they were, because this would expose them.

I don't like that theory at all, because it contradicts several important plot elements.

Black magic practitioners who oppose outsiders - most notably Nicodemus and the nickleheads, as well as Wamps, and the infernal powers of hell in general. Huge portions of the Nevernever are understood to be "evil", with most commonly understood "demons" just being various creatures of the Nevernever.

All of the Outsider hints dropped early in the series - The whole point of Victor Sells, the wolf belts, and all later hints was that Harry is dealing with black magic that isn't behaving normally. They aren't normal bad guys, they are off somehow, and so is their magic. This strongly indicates that there is such a thing as a normal bad guy and normal black magic.

The traditional good/evil moral dimension represented by heaven/hell - The Outsider conflict is one being fought by "the world" headed by Mab against "the outside". The Dresden Files has another conflict between the forces of heaven and hell. This is NOT about protecting the world from outside, it's about the souls of mortals. Uriel and the swords basically treat outsiders as irrelevant to their mission. Instead, they fight evil, and the corruption of free will by the forces of said evil. If the source of this evil was "outside", then they would be set against outsiders, which they are not. Notice how the swords never show up in an outsider story?

Tying black magic to Outside in general kills a huge portion of the nuance of the entire story, and simply does not track with the story overall.

...would the KotC try to break them out? I've heard a theory that the way to trap the Coins in Demonreach is to trap their bearers with them, thus subverting the "meant to be in circulation" issue--they are in circulation, it's just that their hosts can't do anything. The problem with this is that a coinbearer trapped in stasis on Demonreach couldn't repent (I don't think), so it seems like something the Knights would have a problem with.

I think the idea that Demonreach can't simply lock up the coins without a bearer is laughable. The church can't hold the coins because it puts the coins in the hands of free-willed humans. It's like hiding a steak in a dog kennel. Demonreach is not a free-willed mortal. He imprisons things that are WAY more powerful than some pathetic ex-angels, and can't be influenced by puny nickleheads that can't even manifest outside their coins.