Being an "advanced writer" (in a roleplay setting) is also more than the characters that you play. 

It's in the story that you craft with what you are given by a GM, it's how well you can develop chemistry with other writers that translates onto the page and creates something cohesive. It's writing about your setting, creating good prose, could even be foreshadowing, using themes throughout your posts. 

Writing and roleplaying - whether casual/high casual/advanced is so much more than the character that you're playing, but how you [i]give[/i] character to everything else as well.