And who's to say to members from rank:full member and above are all quality/Top notch posters, I disagree with you totally as there are numerous members on that rank,even on well paid signatures but still post poor quality on the forum.
Go to the BD or AD section,and check out threads with numerous pages, the final pages aren't always filled with shitposting noobs, you'll also find the very full members and above ranks with posts in there that are even more worthless than that of a junior member

The problem is with shitposters and not with ranks,putting it out as explicitly a rank problem is rather unfair and saving the shitposting high rankees some sticks.