It occured to me that Drakul could have killed or captured all the wardens, Harry, LtW and River Shoulders.
Harry says he carries more personal power (at least in terms of raw will, if not magic too) than the Lords of the Outer Night. It's unclear if he was including the Red King too, but it seems likely given that Drakul is one of the beings that could have beaten Man in a straight duel.
If he had used his Will to bind or even kill them, I doubt any of them except perhaps Harry could have resisted for long and maybe River.
It seems like the entire point of the tactical contest, at least to me, was to see what they were made of. If they had been to weak he wouldn't have bothered with them. He wants strong recruits surely, hence why he picked battle hardened wardens.
Despite this, I am not sure why the whole charade. Why not capture and turn all of them? Surely LtW would be a target, let alone River. Imagine a Black Court Bigfoot. Would be truly terrifying! Blood on his Soul would look like a cartoon villain compared with that.
Perhaps there was a distraction element for Ethniu too...but LtW seemed to think he didn't really care how the battle went as long as he got what he came for. Three wardens out of all that seems like slim pickings. And the three weakest at that. Especially when you consider he lost two vamps too.
Unless he wanted them for other reasons of course. Perhaps it isn't about recruits really. We know star borns get sacrificed for the stars and stones. Perhaps it's about luring them to him. But then, he seemed rather bored of Harry quickly.
So perhaps it's more like the whole Justin/He Who Walks Behind thing. Perhaps it was one thing meant to look like another. Perhaps it was about twisting Harry a bit...into whatever he is supposed to be.