I've been there a few times first week of Dec and have found the crowds light. One time, Fantasmic wasn't even full. That was the only time I saw that happen.
Only thing is, I think this is around the time of Pop Warner or some other cheerleading event. Though I've found the groups to be well-behaved, others have had bad experiences, especially at the All Stars. Maybe someone else can tell if this is a time for those events?