So not reviewed yet.
My point is that both a preprint and a letter to the editors have not gone through a rigorous review. Preprints might be submitted for peer-review but that's no guarantee that it will be published in a reputable venue.
Yes, both are text, written in the english language, shown on a webpage. Beyond that, they share no similarities.
If you cannot reliably judge the legitimacy of a pre-print in an area, then you aren't qualified to judge the legitimacy of any scientific comment in that area.
> If you cannot reliably judge the legitimacy of a pre-print in an area, then you aren't qualified to judge the legitimacy of any scientific comment in that area.
I agree, but now we are moving into the content and not just judging the book by its cover.