There is no contradiction: from a systems point of view, a single event may not have been enough to have such a massive impact. The fact is, we're not seeing a

There is no contradiction: from a systems point of view, a single event may not have been enough to have such a massive impact. The fact is, we're not seeing a single non avian dinosaur in the fossil record after the event. Same for entire other genuses. If the system hadn't already been destabilized beforehand, we probably would have seen remnants lingering for a couple million years or more. Instead, we see a crystal clear cut off date.