I'm finding it difficult to follow the thread of discussion here, so I'll just blurt out some things:
* Most PRs that come in do indeed get squashed merged, but because of a few reasons. Sometimes it's because the PR is really just one logical change and really should just be one commit. Sometimes it's because the commit messages are not written in a way that I like, and so I do a squash-merge so I can either edit or re-write the commit messages provided by the author.
* Sometimes I do a "rebase and merge" if the commit breakdown is good and so are the messages. It's somewhat rare, but some contributors get it right. I'm fine with a single PR containing multiple commits, but the common case is indeed "one PR = one commit."
* I don't usually levy this criticism because I think it's low-brow, but the OP here---"git commit messages are useless"---is pretty egregious clickbait. Halfway into the article, the OP acknowledges that they aren't useless, but just useless in the context of a PR workflow. Which... I don't also 100% agree with, but is usually true for very small changes. What an annoying submission.