Actually, it does matter, because you're confusing CONTENT with CHARACTER STATUS. Saying that GOTG had great trailers has NOTHING to do with the level of popularity of the characters in it, and has everything to do with the content that was created/incorporated, and how it was portrayed. Nobody (well, almost nobody) cared about the GOTG characters before the movie hit, but it was the quality of the content seen in the trailers and movie that made this film a blockbuster.
If the Ant-Man trailer is "mediocre", then that's because both the trailer and movie itself were created in a mediocre fashion, and has absolutely nothing to do with Ant-Man's popularity status as a character. There have been several comic book movies that revolve around A list characters, that have tanked: Hulk, Daredevil, Green Lantern, Catwoman, etc. You know why they tanked? Because the quality of the content was garbage, and that had nothing to do with their popularity status.
With all that said, care to elaborate how the Ant-Man character himself is responsible for a "mediocre" trailer, or at least contributed to the mediocrity?