User blog comment:TheMoirai/Writer's Workshop: Setting Up Your Story/@comment-1874924-20151202083246

The question of canon vs. OC is to some extent a "know your audience" thing. On this wiki, OC competition stories have reigned supreme for as long as I've been here; and with a few notable exceptions, there's been little interest in noncompetition stories, hence this workshop's focus on competition stories. On fanfiction.net, by contrast, canon casts are more popular for competition stories (possibly because that site doesn't support supplemental OC materials such as artwork or character pages) and noncompetition stories (most notably romances featuring one of a handful of popular couples) are a good deal more common than they are here. Also, fanfiction.net forbids script format outright.

Using canon casts is easier than building a lineup from the ground up, but has its own set of challenges, most notably to adhere reasonably closely to a pre-estalished characterization unless you give a good reason for departing from it. On a related note, be sure your OCs act in accordance with their labels, at least until they have enough character development to justify going in a different direction. I've seen a number of competiton fics where the writer seemingly can't be bothered to do this, which defeats the purpose of having labels in the first place.

Concerning character diversity/distinctiveness: One of the first competition stories I read all the way through was reasonably engaging and well-written, but it did have one significant flaw that the author acknowledged when I mentioned it: the cast was not so much 20 different personalities as four or five batches of clones.