Quality and quantity are both important, because "quantity makes quality".
I don't agree with you on this and I don't think quantity actually makes for quality as I've seen very short post that contained Alot of quality and even earned Alot of merits as a show of appreciation for it's quality.
I'm practically not against lengthy post especially when there is actually a need for it and I also agree with you that the case usage also matters Alot when talking about quality and quantity.
Talking about JayJuanGee, I think we all know he doesn't just make random post but rather takes Alot of effort and time to put out a post and his exceptional.
I think the both of you are not making a mistake in your opinion cause you all are correct but when it comes to short quality post, the ability of the writer to summarize the message or information that is contained in his post in few lines tells how much writing skills he has but nevertheles, not everyone has the ability to summarize some useful information in few lines but if the writer is able to increases the length of the post due to his inability to summarize it in few lines without going off key, I am the quality still counts because of how detailed the information is presented and the message it carries.
A lot of people in the forum has the ability to pass good informations just by writing few lines while others must write very lengthy post to be able to communicate effectively but once they remain inline with the subject of discussion without going off key, I think both writers are said to be good writers regardless of the length of the post they make.