You're forgetting something.
Remember the trailer for Heavensward? Remember how much allusion there was to the Holy See and the Archbishop being the main villains and final boss? Absolutely zero.
Remember the trailer for Stormblood? Remember how much allusion there was to Zenos and Shinryu being the main villains and final boss? Absolutely zero.
Remember the trailer for Shadowbringers? Remember how much allusion there was to Emet-Selch being the main villain and final boss? Absolutely zero.
So what makes you think the teaser trailer for Endwalker gives you any information of who will be the main villains for the expansion? Do you really think that after all these years of being careful with spoilers and not giving away too much plot in advance, Square-Enix would suddenly begin a tradition of giving away the main plot and headliners in a teaser trailer for the finale of the story?
My point being, be patient. We don't know anything about where this is going yet. All of us used to think Ascians were boring and generic too, then Shadowbringers happened. Let's not be too quick to judge Endwalker when we haven't even seen its full trailer or Shadowbringers final patch yet.