Morgan.

I thought his death was pretty close to perfect - the only thing really wrong with it is him changing his position on Harry just as he dies.

Yeah, it's also one of those things that straight up doesn't make sense. You don't use all of your brain for conscious thought, but you do kind of need all of it for a bunch of automated processes.

It's not just that.  The difference between a brain with 10% of the neurons firing, and one with 100% of the neurons firing, is like the difference between a (very big) page with lots of complicated text written on it and a sheet of plain black paper the same size.  One can contain complex information.  The other can't.

It is not a stable peace if one side is plotting the best time to attack the other side.

It is if they have the slightest bit of sense about their assessment of the other side.

On one side, we have the Red Court knowing about the White Council for four or five hundred years, and taking all that time building up their forces to a point where even the most hardline of them think starting a war is a reasonable exercise.

On the other, we have Luccio in Changes noting that the Council has twice the combat strength it did before the disaster in DB.  Which took them about five years.

The Council can stay ahead of any rational Red Court threat indefinitely with a much lower growth rate than they demonstrate themselves capable of.  Therefore, stable.

Humans are vamp food; noone who is hungry likes it when their food gets the ability to fight back.

The most important datapoint we have here is Harry's conversation with Butters at the start of Dead Beat, which establishes that disappearances among humans in the DV are exactly the same as in reality.  Harry thinks that is supernatural predation because he is not in a position to make the comparison, but the DV is shown to have crime, and abusive families, and generally the same reasons real people disappear.  The message that conveys is that supernatural predation kills negligible numbers of people.  All supernatural predation, of which the Red Court are a subset.

Which doesn't mean they are friendly kittens.  But it does mean that for the White Council to spend time and enemy spent hunting them, compared to addressing much much bigger problems (the failure mode of not catching powerful warlocks early and firmly, for example, being on record as organising a world war), is gross negligence.

Appeasement is never a solution; it is only a delay.

Viewing it as "appeasement" is most of the problem.

The Red Court and the White Council have maintained a stable peace for four or five centuries.  That's evidence enough that they can continue to do so.

Yet Cowl sure seemed right ready to go through with it once Grevane and Corpsetaker were dead...

Convincing Harry of that is a good way to stop Harry digging any further into what's really going on there, though.

You're probably right on Lea's "magic feather" bit.

I believe there is a WoJ that that was most, but not all, of what Lea provided Harry.

Just finished TIWTBWO #5 about two hours ago, fwiw. Which is just in time to have a holiday season full of socialising and not much writing time to mull over whether I want to try the new thing I have been thinking on (long episodic SF novel starting nearish future and going into very deep future) or going straight into TIWTBWO #6 (which is one logical volume and the conclusion of the second arc, but bids to be long enough that I might split it into two physical volumes.)