There is a fundamental difference of storytelling philosophies between the two mediums. In comics, every panel intended to be viewed with the readers’ attention. Manga, on the other hand, is more about flow and motion. It is a common view with Manga editorial staffs that the viewer should not be required to spend more than 30 seconds per page with a Manga. And I mean per page and not per panel.
With Manga, the art style does not change throughout the life span of the title. Once an art style is fixed, that is it. So, if the existing artist is no longer available, Mangas are either discontinued or they find another artist that would carry on the existing art style. With Comics/Graphic novels, it almost seems that the art style changes every few months while the story continues. For a native manga reader, this is extremely disruptive.
Like all visual mediums, comic and manga are the partnership between story and visuals. However, with comics, the visuals seem to be disposable part of the partnership.
I always wondered why comics gave off this perception. Initially, I thought it may because comics, as a medium, mostly serviced a juvenile audience. However, this is the same with Manga. In some ways, a lot of manga targeted a more adolescent audience than some of the more mature comics.
After some deep thoughts, I came up with a different conclusion. The reasons why comics can feel pretentious lie with the presentation of the story rather than the story itself. First, because of the nature of the medium, a complex story is crammed into very few pages. With manga, a story line can cover more than a thousand pages. For example, a sports series, Slam Dunk, spent about 5 books to cover a single basketball match. That is more than a thousand pages. Second, because of the overreliance of monologue and exposition to present the story, the message of the story feels preachy. Third, the lone gunman nature of the superhero genre creates a mismatch in scope between the actual plot and the message of the story. These cause the story to feel pretentious and pompous.