The point of forums such as this one is to share information, learn from each other, solve problems, enjoy talking to people with a common interest. The usefulness-factor is high: finding solutions, learning, teaching. So imho, a post is a good post if it gives enough information in a clear manner to be understood and useful. If that can be done in a single sentence, fine. If the single sentence creates confusion or misunderstanding, then it is worse than useless.
The post being criticized for its length was the one by Liw. His posts are usually well thought out and contain useful and pertinent things. This one was no exception. Otoh, the opening post - clearly written and factual, but what's the purpose? How does it help anyone with anything? At the same time, beginner students is an important topic. I think most people know why. So if we went into it in depth, and wrote enough rather than too little, that's a good thing. Of course if you are not interested in teaching beginners, then it's not a topic for you to follow, even if only a single word appeared in a post.