Sure, but that is a moderated communication channel. They pick and choose what to publish and, unlike most comment sections, unmoderated content is not visible to your audience. The opaqueness of the moderation process in a world without instant mass communication (i.e. the internet) would also likely have made it unlikely for your readers (users) did not have an expectation for their messages to be quickly reviewed or published.

The other big advantage is that the only participants in channel are the newspaper and the submitter; no interaction between third parties on your platform means no flame wars or the like.

Sure, but letters to the editor required the paper to read them and choose which ones were worth printing.

Comments on most news sites are typically just assholes making every story about whatever they're obsessed with.

Letters to the editor are still an active thing.

Yes, but letters to the editor were picked by the editors for their ideas and for their writing. It was a high bar, often higher than the newspaper itself. So I used to enjoy reading them because of this.