I don't want to cite sources and you citing sources and getting into a mess. But Duncan is too "plastic bum sprayed". Connor looks like the real deal. For some awkward reason Highlander II is my favorite b-movie.
The first Highlander movie is just a masterpiece to me. And then...every sequel contradicts the previous one.
Ok...
Highlander - is perfect.
Highlander 2, Highlander 2 Renegade Version, Highlander 2 the dvd (forget title but with sky color different and loads of extras) has immortals be aliens, travel to time - favorite line "they will be send in the future to leave eternally, thus, being their punishement" - wow - I think I could deal with that. Old Connor kills an immortal and then his youth comes back???
Highlander 3 is good but is basically a remake of the first one with...no punch at the end.
Highlander 4 (with Duncan) where is Connor's adopted kid? And now, we have 53 rules that we didn't have before.
Highlander 5 - ouch...that one is really bad...
They are not the same person but are the same - Lambert not being there and Panzer/Davis wanting to keep the name "Highlander" to have at least a fanbase (and it worked) made up a new character - who...basically is the same. You'll notice if you watch one the shows that it says the characters was created by Greg Widen too.
Duncan is choice #2 because choice #1 was not there. And over the 6 years of shows (except season 5 had less shows and less shows in 6 and a lot of them did not include him) they had time to develop more background stories. I found Adrian Paul to be quite good at comedy. And of course his sword fights were amazing.