Quote Originally Posted by Dorander View Post
It's entire purpose is to showcase the titular job of that expansion.
Correct. As well as showcase the main NPC players on the stage. Heavensward was dragons vs dragoons, as well as the upheaval of the city states. All of which were represented in the trailer. (And if we want to talk about inaccuracies, look at the dragon in the HW CGI trailer.)

I believe the Stormblood trailer is showcasing monks (maybe even opposing philosophies of said monks) as well as Yda (or her sister) training to fight for her people. But that's just speculation.