That's the point: the film already has elements rarely associated with the history of Cap stories (acknowledging the MCU has not been big on tight adaptations of comic book stories or character legacies...still...). Tossing more Hulk-related elements (Red Hulk, the Leader, possibly the Banner Hulk, et al.) feels as if its crowding out the kind of story Wilson would need for his first solo story.
It's been well-established the only reason that the MCU hasn't done another Hulk film is because they can't buy back the rights from Universal, right?