I don't mind the Kiffin takedown, but Finebaum was far from the only person saying those sorts of things about Kiffin while he was at USC. Kiffin's reputation was hard-earned at that point in his life.
I don't for a second think Finebaum couldn't have fired back with a few things. "I'm good at keeping my job" would have been a great escalation. But Paul is a good company soldier, and moreover, is almost never confrontational or aggressive in interviews, so - had to tuck that tail and take it on the chin. There was no world where he would, or even could, have said anything serious back.