I hope that part of being accepted into a PhD programme involves the ability to realize that there’s not much room at the top.

Personally I loved my PhD experience even when I knew that the race to tenure was not for me. In many ways the reward of a science PhD on the jobmarket is large. At my current company we are treated as superstars among both engineers and management, and there is plenty of ways to make use of whatever lessons learned. (Disclosure: experimental particle physicist working in the European defense industry).