Well I'd like to see you actually argue that Orton's diaries are
'the best thing he wrote (by some distance)' instead of just baldly asserting it.
In his suicide note, Kenneth Halliwell, Orton's lover and murderer, wrote: "If you read his diary, all will be explained. KH PS: Especially the latter part", so maybe they were meant to be read, rather than to be published, in the first instance.
I didn't know that Williams published
'a sanitised 'version' [of his diaries] during his lifetime' - could you elaborate please?
Certainly in a TV interview that Williams gave with Mavis Nicholson (which I can no longer find on youtube), KW is rather taken aback by her suggestion that he wrote his diaries for publication until she clarifies that she meant for publication
after his death, whereupon his says something like 'oh well it wouldn't matter if they were published when one is dead'.