It might be useful to review the official synopsis for Thor1, which was released about 1 year prior to the movie's opening (a similar interval to that for the synopsis for T:TDW that we are currently discussing relative to that movie's scheduled release):
"Paramount Pictures and Marvel Entertainment present the epic adventure, 'Thor,' which spans the Marvel Universe from present day Earth to the realm of Asgard. At the center of the story is the mighty Thor (Chris Hemsworth), a powerful but arrogant warrior whose reckless actions reignite an ancient war. Thor is cast down to Earth by his father Odin (Anthony Hopkins) and is forced to live among humans. A beautiful, young scientist, Jane Foster (Natalie Portman), has a profound effect on Thor, as she ultimately becomes his first love. It’s while here on Earth that Thor learns what it takes to be a true hero when the most dangerous villain of his world sends the darkest forces of Asgard to invade Earth."
Loki is villainous, evil even, and the Destroyer was a threat to Earth. But we probably could make credible cases that Loki is not the *most dangerous* villain of either Asgard or the Nine Realms (depending on how you define "his [Thor's] world") and the Destroyer probably is not the *darkest* force of Asgard.
So we probably shouldn't put too much weight on any of the particular descriptors; at least some of them probably are there to make the movie sound more exciting.