I've been musing on this, I'm not sure I agree with the idea that the Bashir interview created a 'false narrative'. Obviously Diana was lied to, which is appalling, and I'm sure that fueled some of her paranoia but isn't it true that she was spied on at times e.g. with the squidgygate tapes? And she'd already collaborated with Andrew Morton saying many of the same things, and apparently wanted to do an interview after Charles gave his.
I don't know... it just feels odd to me that William is essentially asking for it to be struck from the record. He was apparently angry with her after the Bashir interview and was teased about it at school, which must have been horrible. Is he trying to protect her memory or is there an element of trying to tidy it all away?