I don't think Barr has said or believes a four page letter could fully capture the context, nature, and substance of a multi-year investigation that concluded with a 400+ page executive summary, let alone the vast quantities of supplemental evidence and testimony gathered, and ongoing criminal investigations. Barr's letter wasn't the end of the line, it was the first step in the process of releasing the report. This doesn't even seem particularly weasely to me.
I'm sure you aware that quote goes on...Twitter Link
Two lies.
The letter was made public under two months later.
He doesn't give a shit. This is what impunity looks like.
"I think, I suspect that they probably wanted more put out. But in my view, I was not interested in putting out summaries or trying to summarize because I think any summary — regardless of who prepares it — not only runs the risk of being underinclusive or overinclusive but also would trigger a lot of discussion and analysis that really should await everything coming out at once."
...which very much sound like what Mueller was saying in his letter.