My point of view , just to take some emotion out of this. This is one account of one person's relationship with another. It's a memoir.
As an historian (I'm not but am used to reading with an analytical eye ) , if you read a memoir , diaries etc , you do it with an eye to the bias of the author. & if you are doing it academically , you find other texts which either substantiate or oppose the author. Also , why is it written ? Is it for history , money , to set the record straight, for the benefit of the legacy of the author or any one of those or another reason. Which subsequent people will have to analyse and decide over time where the real story lies. Now eg if you were analysing the dairies of let's say Churchill or Nelson (I'm making this up here - but bear with me ) there would be people who think because of the historical context it is worth doing. Over time will CS's memoir be worth analysing - no idea.
In this context also, in the context of the whole book ( which I have not read ) are these headline snippets reflective of the whole book? Or are they the crowd-pleasing bits which CS can sell to the DM for its serialisation.
I'm not saying CS is right or wrong - All I'm trying to say is that CS has written a personal account. No-one can necessarily make a judgment about either he or KC being "dreadful" . It's a new book and it's newsworthy but without being po-faced , memoirs are just those. Not necessarily everything in them is fact. If they go towards a body of work which comments on a particular period or group of people , all to the good. But to be taken if one is interested in trying to get as near as possible to the facts , as part of a whole.
As an example @bluegreygreen has given a contemporaneous reference regarding the walk behind Diana's coffin. This is one example of how one memoir has to be taken in context.
OK I realise I have been rather a bore there . Sorry 😊