I'm not sure off-hand what percentage of a whole is needed to give a representative sample, but the forums represent around a 1-2% section of the playerbase for the server. I don't think that's necessarily a blocker for polling as 20,000 people could be used as a sample of a 20,000,000 heavy populace.
Samples are often generated through random selection of the whole to avoid a biased section over/under-weighting an opinion. The forums draw the attention of players that are, for lack of a better term, forum-goers. That by nature is a subset of the whole as 98+% would not fall under the "forum-goer" group innately as they don't frequent the forum.
The views and concerns mentioned here are recorded. We take feedback from anywhere it exists and the forums are quite literally one of my main work areas. It's just worth remembering that an oft-repeated point on a forum is an oft-repeated point on a forum as opposed to a resounding cry from any and all walks of life. Common pain points regarding CVs, Subs, Matchmaker, and more are voiced in many places, which echoes forum sentiments but isn't proved simply by their existance in this one place.