Look Lobsel, it's obvious you and I are approaching this issue from different perspectives, so let me pose you a question. Do you think Briala's Fen'Harel gambit will help the world defend itself against the demons? Do you think teleporting elven assassins weakening the strongest nation in Thedas will improve our odds of sealing the veil tears? Will a nascent and unstable elven nation be more beneficial to our cause than the Orlesian Empire?
Serious question, I want to try and understand where you're coming from.
I'm coming from the position that the choices may be left in the hands of the player, rather than dictated to us. The veil tears need to be closed, but that doesn't necessarily mean the Orlesian Empire is mandatory to achieve that end. The Highlands is optional, and this may extend to a plethora of other choices.
Frankly, I'm looking at this from the perspective that some players may want to ally with Briala because her goal aligns with their protagonist's own. It's not about what's optimal, but whether or not the Inquisitor would be willing to take the chance to use his (or her) position to bring about change.
For example, I think the Dalish Inquisitor could have reservations about helping the Orlesian Empire, given what happened to the Dales. If Briala is offering an alternative in helping free the elves, it's not implausible to think some players would prefer to pursue that, over siding with Gaspard or Celene.