Absolutely a very thoughtful explanation of the entire forum I guess, but if I must be honest, there's really no Quality post, and if there's, they're just few. What I found here on BTT Forum is informative post, which I think most people refer to as quality, we need to learn the difference, because everyone is just after quality post, they write heavens and earth all together, but one informative line, it's enough to spike a superb light in the live of forum users
Imo there is absolutely no difference, a quality post is one that has ample information about the existing subject/topic of discussion, meaning that is an informative post, i don't know why you are differentiating the both of them when there is definitely no difference, they can both be considered synonyms in this context and can be used interchangeably without any confusion.
I'll add that a quality post is a post with references to the source.
I don't see how that makes a post a quality one, and only posts that are extracted/copied from somewhere requires a reference/citation to the original source.