Did you have to sign a NDA? Because if people send you random advice via email after reading a blog post then this sounds to me very much like "publicly sharing" their experience...
I disagree. It's a private email. Gitlab can ask permission to post, but it would be impolite and perhaps unethical to assume a private email is now "public". If they wanted it public, they could have chosen to provide a comment on HN, Twitter, etc.
Exactly, everything is private unless it was posted in public by the author or explicit permission was given. We have a transparency value, but we understand that other organizations are different. And even we assume that our private communication will stay private.
Apparently according to syste some of the best arguments came from emails, so he could have put those arguments anonymised and trimmed down to the main points into the blog post, which would have respected the company's privacy while still sharing good arguments, unless there was a NDA which would prohibit that.
So I disagree with you, because you look at this very black and white while the reality is grey.