You're assuming the scene in the trailer where we fight ElidiZenos is the 4.5 conclusion to Stormblood. In my opinion, I believe that the scene in the trailer has yet to occur. The battle at Ghimlyt Dark has yet to conclude, and Black Rose has yet to be unleashed. If you watch the trailer again, you'll see pretty much EVERYONE is dead, both Allies and Imperials alike.
As the camera pans, we see all the allied flags burning, before the camera pans and stops momentarily on a burning Garlean flag. The implication here is that some time has passed since we were defeated by him, and we return to the battlefield amidst the devestation of the Black Rose, which killed both sides. We challenge ElidiZenos one last time and he finally falls (in 4.5 he doesn't fall, he defeats the WoL and nearly killed him). In the trailer, we see he collapses, and we walk away victorious.

The bottom panel where we defeat Elidizenos has yet to occur in 4.5. This is, of course, unless the trailer is inaccurate (HW trailer showed a bunch of Dragoons fighting the Horde which we never saw in MSQ, and it also showed a fleet of Hraesvelgars invading, which was probably a stand-in for generic dragons)