> In this case, the flawed proof/paper was peer reviewed. Making the reviews transparent wouldn't have mattered because in the end the paper was published. Maybe one of the reviewers raised the issues but it was published anyway, so published reviews would tip a reader off?

I don't assume that what you describe would not happen if the reviews were published as commentary; but I do imagine that the public nature of reviews would encourage more careful review, since in that particular case you mention the reviewer and the author(s) together would share the blame for the error.

Additionally, knowing what was reviewed would indicate what was not - and in your example, perhaps there was no careful review of the notation being used. That would be valuable for a critical reader to be aware of. I could read the article, see which parts were critiqued by the reviewers, and if I was skeptical, my critical analysis would build on the reviews instead of reinvent that wheel.