ORD's juniorness is artificial and temporary. They needed to fill the base and had bunch of withhelds they were not going to use yet so they used new hire class drops to basically fill the majority of the base. Once those withhelds get released it will be a while before anybody new gets ORD320 and when they do will be junior for a long time (along with those new hires in base now relative seniority plummeting). ORD is typically a senior base all around.