tl;dr No, just kidding. People have been speaking in short sentences for a long time. Your model is too simplistic - writing letters is a less a discussion,

tl;dr No, just kidding. People have been speaking in short sentences for a long time. Your model is too simplistic - writing letters is a less a discussion, and more debate. Ordinary everyday conversation is shorter, and possibly, more inane. With discipline, I think, and an appropriate community (like Alex mentions) reasoned debate and discussion is possible, without writing pages and pages. See, for example, HN. (Yes, people write comments of this length on other sites, too. No, they aren't always as reasoned.)