"Marvel's Inhumans," a superhero series that began airing on ABC in September, seemed to have it all. The story of a royal family of superhumans comes from classic 1960s comics. The cast includes Iwan Rheon, the Welsh actor who played the ultimate bad guy, Ramsay Bolton, on HBO's "Game of Thrones." The show got a promotional boost from a unique partnership with the theater chain Imax Corp.

The audience didn't materialize. An average of 1.5 million nightly viewers in the coveted 18-to-49 demographic placed it 87th among broadcast shows. Critics ripped the program for its unimaginative plot and weak characters.

The long-running rivalry between Marvel and DC Comics, which began on comic-store shelves and has been most prominent in movie theaters, has now reached the saturation point on television and streaming services. There are more than two dozen superhero shows on the air or in development. The surge is raising the risk of superhero fatigue.

There have been three cancellations among TV's superabundance of costumed heroes: DC's "Constantine," "Human Target" (also DC) and ABC's "Agent Carter." ABC, which also broadcasts the Marvel-based "Agents of SHIELD," hasn't said if it will pick "Inhumans" up for a second season.

Channing Dungey, who heads entertainment programming at ABC, said she remains undeterred by the "Inhumans" experience and will continue to delve into the superhero genre: "I would never say we're through with superheroes."

While Walt Disney Co.-owned Marvel has seen its superhero films outdraw those from Time Warner Incorporated's DC Comics at the box office, the balance of power appears more even on the small screen. DC kicked off the modern era of superhero TV with "Arrow" on the CW in 2012. That show, about an archer whose quiver is packed with trick projectiles, is now in its sixth season and anchors the "Arrowverse" of spinoffs on the network, including "The Flash"' and "Legends of Tomorrow."

Indeed, no channel has staked as much on the genre as the CW, a joint venture between Time Warner and CBS. Its newest production, "Black Lightning," premiered recently featuring an African-American superhero who shoots electricity.

While superhero shows have struggled on the big broadcast networks, they seem to have found a better home on streaming services, where the language and plot lines can get edgier. Netflix's strategy was modeled after Marvel's super-successful "cinematic universe," with interlocking plots and sharing of characters. The collaboration produced some of the most critically acclaimed superhero shows in "Daredevil" and "Jessica Jones." But the Marvel-Netflix relationship is in flux now that Disney is looking to produce new content for its own online video service launching in 2019.

There are likely to be even more superhero shows ahead. Disney Chief Executive Robert Iger has said that gaining more control over superhero franchises such as the X-Men, Fantastic Four and Deadpool was part of the thinking behind his $52.4 billion acquisition of the entertainment assets of 21st Century Fox.

"The audience will tell you when the fatigue has set in," said CW President Mark Pedowitz. "If you have a quality show or a fun show, the audience will stay with it."