Sounds to me like customs really dropped the ball. Making OP wait for all bags off might be a valid action. But still should have left him with enough time. And given that they made him wait, they should have expedited him once the plane was empty of bags.

DL owes for the bags, and likely will cough up some SMs. Alas OP's chance from getting compensation fron US Customs is near nill.

EDIT: Though I am not sure what there is to expedite at customs. Not really much of any line or delay.