You add some great points David.  Thank you

I think we each have our own leadership "fingerprint".  The elements may be the same, but the expression can take many forms.  Your example of the contrast between Mandela and Immelt is a good one.

You definitely don't have to be THE leader to be A leader in any given moment, yet as you point out it is the frequency of those acts of leadership that has someone start to be identified with the label of "leader".

Choosing (or inventing) a definition is very useful especially to use as a guide or compass for our own leadership development.  Rather than focusing on getting to THE one best definition I think we are better off choosing one that as you say "works for me".