Is it appropriate to mention personal lessons learned in the defense presentation?
A bachelor's or master's degree is about the knowledge that you have gained. A Ph.D., on the other hand, is about the knowledge that you have contributed to humanity.  As such, the defense is not really about you: it's about your work, and you need to treat it as such.  Think about the other high-level scientific talks that you have seen (or given), and treat your defense in exactly the same way.

That's not to say that you can't weave in personal experiences or anecdotes if they make sense as part of the presentation of the technical content.  Some of the best talks that I have ever seen have a component of the personal in them.  The important distinction is that any use of the personal should serve to illuminate and illustrate the scientific point, rather than standing apart and distracting from it.