Yeah, it's unfortunate that Firefly never got the chance to deliver there. That said, if you pit the first season of Firefly against just the first quarter of Citizen Kane, which is really more fair in some ways, I'd go with Firefly any day.
I don't think "the chance" is what it lacked. Firefly was relentlessly light and couldn't have sustained the darkness necessary for real moral ambiguity to work.
