CSes are absolutely an application where the GM can gauge someone's writing ability and get a feel for the character. You can find out if there's fundamental flaws with the character (e.g. are they a terrible Sue? Does the player go out of their way to make them overpowered? Is any effort put into it at all?) And while it's not perfect, it cuts down hugely on issues you may run into for games. 

If you have stuff you want to keep secret from the other players, PM the GM and get their approval. There should be no secrets from the GMs.

People like to make false equivilencies between roleplaying and novels, but I disagree. Roleplaying at its best involves a GM that is dedicated and keeps the game moving as well as giving players material for their own posts, and players are all of similar skill and expectations. This is exceedingly rare and people get into spats, do things that disrupt the game, GMs go absentee, etc. The joy of reading a novel is reading a self contained story and being surprised by what the author throws at you. Roleplaying is several voices and ideas being mashed together and you're lucky if it lasts long enough to really get started, let alone hit the surprise twists and character development people expect. But let's be honest; things rarely go smoothly. Post turn over is slow and it takes ages to finish a very simple mission, let alone an entire story arc. You can't keep reading if you are caught up until others post, and the fact there's gamey decisions and GM dictation makes roleplaying way closer to D&D than a novel. 

If you have expectations for novels, write and read fanfics. Don't complain if a GM demands a comprehensive character sheet because it's at bare minimum a quality filter and if there's multiple people interested and applying but you want to keep the RP on the smaller side, character sheet and character quality are going to be the deciding factor. If you don't like it, then don't apply for games where the GM expects detailed sheets or run your own game. 

EDIT: Sorry if you read this when there was a boatload of typos. Turns out typing on a phone between reps at a gym is not exactly the pinnacle of typing conditions.