You've inadvertently made my point. Every postdoc thinks that the academic track (straight to tenure and maybe dean!) is for them, since they 'made it' to the postdoc stage. It is possible that the postdoc struggle [e.g., a second or third(!!) post doc] is a sign that the person isn't cut out for the academic career. Ask a well-respected, well-funded tenured professor what their postdoc was like. Then ask a struggling assistant professor. I think you might get different answers, and I believe these answers are predictive rather than random.