In the defense of The Flash, I've got to say this:
While Wonder Woman has a Greek myth vibe and Aquaman has fantastical imagery, I really think that the appeal of The Flash is mostly character based.
On the surface, The Flash has powers that are overshadowed by a hero like Superman. But I think why people liked Barry and Wally was that they were likable characters done as just normal people involved in extraordinary situations.
Same thing with the Rogues; on the surface, they're cheesy but that's the point. They're a bunch of rejects, and they're rejects who are both self aware and have a 'code'.
I feel like, with the world that Geoff Johns created with wally and most recently Barry, this could have the same tone as The Incredibles. A colorful world with colorful characters; so you're either go with it or you don't.
Also, Aquaman, despite the potential on how cool he could be in a movie, has a very very tainted public image. WB has to go all the way to really fix it. Even in the comics, he's somewhat underused. Hell, Wonder Woman is really underused as well.
The Flash has the upper-hand in the printed department. Despite some ups and downs in recent years, it's just going up now with the new series.