You're right, I either misread your comment or got confused with a different comment or something.

But I do think the Mitsui point is relevant; in particular, the claim that the citation is supposed to back up is:

"Moreover, even assuming that Heppner intended to share these communications with his counsel and eventually did so, it is black-letter law that non-privileged communications are not somehow alchemically changed into privileged ones upon being shared with counsel."

But the distinction Mitsui is actually making is rather different: between communications "for the purpose of obtaining or rendering legal advice" and not; that's at best orthogonal to Rakoff's claim; and the other two cases I mentioned pretty explicitly make the opposite case: documents written with intent to share with counsel, and then actually shared with counsel seeking legal advice, are in fact covered under privilege. The assumption being that the documents are not "pre-existing", they're created as part of the process of communicating with counsel.

But yes, I agree that the "third-party" point separately undermines privilege in many contexts.