> Why did you write so many words then?

I wasn't claiming to be succinct.

> The sentences he writes to explain why he doesn't consider further correspondence fruitful seem genuinely thoughtful to me

I agree, and I don't say otherwise. I still though don't agree that someone else should characterise the piece as "succinct" because of that thoughtfulness. These are different qualities of writing, are they not?.

> The letter in question here doesn't have a sentence that is irrelevant to Russells perspective.

Yes, it's a good concise argument, to third parties who read it. I see that. It's a different thing to a succinct reply to Mr Mosley - that is what the words "in some ways" mean in the comment above.