Odin pretty much hit the nail on the head. 

I'd expand on his point further and say Free, Casual, and Advanced are no longer “writing levels” as they were once described at the height of the site prior to Guildfall. These sections are more like audiences based on commitments, perceived dedication, and social circles. The idea that there is a sense of pretentiousness and elitism in Advanced is no longer a true thing and casual has steadily been improving for over four years now; the average casual RP is yesterday's advanced RP and you can tell that if you read some older threads and archived posts from the site prior to 2014 and compare them to the average thread. 

As for the niche, outlier subforums like arena, tabletop, and nation? They have their circle of those interested in them, but a lot of them are very orientated toward a certain attitudes and groups. There are good writers and roleplays in all three of these sections, though for my taste it can be hard to find them from time-to-time.