So starborn have to be sacrificed at the stars and stones right ? RIGHT
Think about it, Lea tells Harry to never let Mab  bring him to the altar. And repeats it again in Changes. I don’t think that warning is about him becoming the Winter knight.
There is an old WOJ that Drakul is something inhuman stuffed in a human body. And he is a starborn. Hold that thought.
There is a theory going around that the Red King and Pa Wraith are also starborn. Evidence for this is a) for Pa Wraith the outsider protection thing he has. According to the theory he was a starborn of a previous cycle. Hence his expertise on starborn. He was sacrificed and came back with something extra. The defense thing he has.
As for the Red King his entire motif just gives outsider vibes. Lord of the outer night. Anyone?
Back to Dresden. In the BAT, the Winter Queen has to sacrifice a Starborn. To keep reality going.  Hence she takes Harry to the altar and sacrifices him. The he comes back an  immortal with something stuffed inside him. This would explain Mab’s advice from BG.
This can explain why Mab wants Harry to kill Molly. She won’t be able to kill Harry a second time this soon.
It also explains a lot of things such as why Harry keeps getting things that whisper in his head. First Lash and now the mantle. Its Uriel helping to prepare Harry for whats to come.
The question becomes whats going to come back with Harry.
But remember that just a Theory a Conspiracy Theory

I have a WAG that Mab took a direct hand in pulling the wool over Harry's eyes, there.
She wanted him checked, less-willing to play fast & loose with the rules.
So she explicitly whammie'd him in that moment.  Act of Mab, not an act of "Winter Law."

It could be but my guess is somewhat different
Harry shouted fuck winter law in front of non winter beings. Embarrassing Mab and Winter in the process. To disobey Winter law requires subtlety. Wc Harry clearly lacks

Thank you, I think.  But I'm just trying to think like the character would think.  As Harry says, his nerd .... er junk is larger than everyone else's. 

1 of my favorite things is people calculating feats eg Deathbattle
On that note, Harry does ruin dnd campaigns with the wolves by calculating how much energy each feat such as a fireball would take. Will and friends dont like it

My issue with the paranet is thaf its too loose anyone cn join. Paranoid Gary. That guy will upset something/someone and require protection plenty soon.
Who is in charge

It wasn't even a big genocide just a tiny one. It actually how i go in to the series. A friend was like the books are great, Dresden kills those who mess with him, burns those who mess with is friends and kills your whole species if you mess with his daughter. I was sold on the books

Given his behavior. Invading nations, disregarding rules of law he would fit right in with the rest

No, you wouldn't have a '4 star general' to give a single individual their orders... Each court would need 4+ knights with banners for the Ladies to be 4-star generals to them.

I think that you are right in that the Mantles weren't meant for the last ~1,000 years, they were meant for what is coming next and they have just been holding power intended for others (Harry and Molley for example) to use.

The real question in my mind is were the Fae Courts split in two to prevent the powers of the Knights, Ladies, Queens, and Crones from being used at all? Divide a power in half, give the two halves to different people and set those people at odds with each other to ensure that the power was used to counter itself and not to an end.  If that is the case then Harry will claim the power of the Summer Knight as well to re-unite the mantel and use it for it's true purpose, and Molley will reunite one of the Fae Queen mantels (both halves of the Lady mantel or both halves of the queen mantel).  Unifying that power so it works to one purpose being required to hold off the Outsiders in the conclusion of this generation of the push.

I don't think the powers can be unified. The OG being in my mind was Death on a Universal scale maybe Entropy itself. Then  to interact with creation in split it self. MW getting something like 50.1 and MS getting 49.9. Wc would explain why the OG MS can retire. While MW has not. The Queens then were split off form the Mothers. Following them the Ladies and the Knights.
The Ladies in my view are meant to be the Knights director  giving the Knights orders and information about when and where to strike. 
The Knights in my theory are meant to introduce new battle strategies and techniques. Teaching the armies that the Lady recruits how to use modern weapons.
In Harry's case teaching winter Fae to use flamethrowers. Imagine harry going ' the gates of reality were were burning it wasn't my fault.
In all seriousness I think the Knights are meant to introduce new innovation to the courts.

OG Merlin either stole it or won it in a bet the same way Harry in Cold Days won the Wild hunt in. Power cant be given, in freely. MW is among the most powerful beings in the universe. Noone steals from her with out her consent. Similar to how Harry and co stole from Hades