Dryptosaurus was fairly large, maybe 7m, and I assume hadrosaurs were the principal prey for any top predator in the east. There apparently were no large ceratopsids or sauropods.
*Dryptosaurus* retained an extra-large thumb claw. It clearly did something that tyrannosaurids didn't do.
Maybe it relied on its manual claws to catch and kill hadrosaurs whereas tyrannosaurs relied on their jaws.