From the trailer, I'm not sure it's possible to see it in terms of "this part happens in present day, this is the past" etc.
In the new Famitsu interview, they say there is a deliberate presentation shift away from direct story telling to a more themeatic display.
https://www.reddit.com/r/ffxiv/comme..._interview_of/
Q: I think the trailer switch from the Hollywood style, to a more theme-oriented European movie style.
Y: Absolutely. Our target is to make our audience to not entirely understand what's happening, but still can enjoy a sense of epicness.
With that in mind, as others have pointed out, the Amdapor bosses may just be a representative of light, and how the WoL - throwing themselves at it again and again - is constantly rebuffed. Only the switch to Darkness / Dark Knight overcomes this "foe".
Another thing, I wondered about the visions the WoL is having. Premonition or flashback? It's not clear, naturally. He is, however, initially shown as his 1.0 archer, in a land reminiscent of Mor Dhona. There are crystal formations that can be seen at the start. Themetically it is a good place (if indeed it is, and not just some random wasteland, also highly plausible), because it is where the WoL's story started (for 1.0 players, at least).