On this note, I think Onyxia was added solely to give the quest some spice besides politics. Also a dragon tie-in, but it meant a ghost dragon to fight at the end as opposed to a single sorcerer. They definitely needed to have some intrigue to the questline besides the politics: even if you argue the Orc one did that without magic bullshit, there are still ghosts and a billion alien orcs from another planet.
Also the quest differentiates the "true Defias" as people that still want to fight and do good as opposed to the "thugs" that Vanessa mentioned sticking around just to cause sufering. It's just that Vanessa tells the true Defias to go home, likely because there aren't enough of them.