10 worst mistakes the Arrowverse ever made, ranked
5. Dropping the ball with John Diggle's Green Lantern arc
The culmination of Arrow genuinely surprised fans when it alluded to the possibility of John Diggle becoming the Green Lantern. It was a storyline audiences had wanted to see for years while the series was more interested in focusing on what he could add as an original character. But in the end though, the series finale left us with one heck of a cliffhanger.
It would have been fine if we never saw Diggle again after that, because that ending is brilliant. But we do see him again, with occasional guest appearances on Batwoman, Supergirl, and DC's Legends of Tomorrow that only reference the box that fell out of the sky and chose him. It was his appearances on The Flash that really dropped the ball, because they ended with the character ultimately deciding against that life.
While it works for the character of Diggle because he'd rather stay on Earth and be with his family, it just highligths how much of a wasted opportunity the tease was. Why did The Flash feel the need to address this arc, especially when it was going to end in such a disappointing way?
Showunner Eric Wallace revealed that Diggle's decision was engineered to wrap up one of the few loose Arrowverse threads before The Flash brought the shared universe to a close, but honestly, it would have been better if they left it alone. The mystery of Diggle's future as the Green Lantern was far more exciting.
With the exception of his final appearance on The Flash in season 9 (and the other Diggle that appears on Superman and Lois), we really didn't need to see Diggle again after the Arrow finale, because that was a fitting end to his arc.