I guess from my perspective you can't buy the S or the X in Australia, all I see everywhere are the 3 and the Y. So for me its not flagship but I do know that the S was the original popular Tesla and has all of the bells and whistles.
The S was a true American "land yacht" in the classic style of an Oldsmobile. There's a lot of reasons for it to be seen as the US flagship model and for it to have done poorly in other markets or not even released to them.
