Gabriel, you know that this is not an offense. We know each other too long. But in Germany, the term "Flugkapitän", in English "flight captain" is not only the word for the human with the four stripes on each shoulder in the cockpit.
I hope we agree when I say that an aviation beginner, i.e. some one who's never sat in a jet cockpit, does not begin with a B744.
Thus, for me at least, a flight captain in a B744 is more than a flight captain in ... let's say a CR9. A flight captain has enough experience, in years and in flight hours, to show a pilot with zero flight hours on that type how that a/c type is flown. Les Abend is only an example.
So, in my naive imagination, a B744 Flight Captain is some one who is able to explain a 747-400 to, let's say, a CR9 flight captain.
747-400 flight instructor might be a synonym. And in my humble opinion, you can't explain a 747-400 to someone else after only five months or less than 900 flight hours in the cockpit of a B744.
PS: Would you trust a driving instructor who is only 16 years old? A little bit exaggerated, but I'd bet, you wouldn't. And I know a little bit of what you do.
In Germany, there exists the word "Kapitän der Landstraße", which again is not used for somebody who gained his drivers license 5, 8 or 9 months ago...