>>94675717*facefuckingpalm* Without Dan, R&M wouldn't exist, seeing as how he writes like 80 percent of all the scripts. Justin is just a voice actor who spitballs plot ideas, he doesn't actually write the show, nor does he have any knowledge or experience in television production.
Seriously, just watch like any random episode of Community or the Sarah Silverman Program and you'll automatically be able to pick up on Dan Harmon's writing style. Dan may be an emotional train wreck, but it's that emotional instability that makes this show popular in the first place.