Warning: Contains spoilers For Fantastic Beasts: The Secrets of Dumbledore.
Fantastic Beasts: The Secrets of Dumbledore is the second time the opportunity to use a forgotten Harry Potter character and explore his interactions with two key family members has been wasted. The third film in the Fantastic Beasts franchise takes the focus away from Newt Scamander (Eddie Redmayne) and follows Albus Dumbledore (Jude Law), as well as his two relatives: Aberforth (Richard Coyle) and Aurelius/Credence Barebone, played by Ezra Miller and later revealed to be Albus' nephew. Despite this, it neglects to explore these dynamics in great detail, repeating a mistake made in Harry Potter and the Deathly Hallows Part 2.
Following on from Fantastic Beasts: The Crimes of Grindelwald, Secrets of Dumbledore sees Albus Dumbledore uncover the mystery of Credence Barebone, ultimately revealing the young man to be his nephew, and the son of his brother, Aberforth. Albus and Aberforth's relationship is frosty, after an altercation between the men and Gellert Grindelwald previously ended in the accidental death of their sister, Ariana, years ago. Aberforth hosts Newt Scamander and his brother, Theseus, at the Hog's Head Inn, where Albus shows them his blood pact, which prevents him from directly antagonizing Grindelwald. In Harry Potter and the Deathly Hallows Part 2, Aberforth helps Harry, Ron, and Hermione by smuggling them into Hogwarts, and later aids in the Battle of Hogwarts.
The Wizarding World movie series has wasted Aberforth Dumbledore twice, neglecting to explore his complex history with his brother and Grindelwald in any detail. Though the brothers share a brief conversation about Ariana's death in Secrets of Dumbledore, it is a fleeting mention and does not thoroughly dive into how Aberforth dealt with the trauma of losing his sister, potentially at his own hand. Writers JK Rowling and Steve Kloves could have let the brothers share their grief, perhaps through a flashback. Instead, the scene ends abruptly with Aberforth making a snide comment toward his powerful wizard brother, Albus.
Revealing that Credence Barebone is Aberforth's son makes the younger Dumbledore's relatively minor role in Secrets of Dumbledore even more baffling. The film reveals that Credence is actually Aberforth's child in a very rushed way, almost as if the screenwriters wanted to hide the previous twist (that Credence/Aurelius was a Dumbledore brother), due to some viewers not liking it. The fact that Aberforth and Aurelius share only one scene, as the latter is dying due to his life being drained thanks to him being an Obscurial, makes Aberforth's lack of focus even more egregious.
It seemed somewhat reasonable that Aberforth's role was minimal in Harry Potter and the Deathly Hallows Part 2. Albus had already been killed by Snape, and Harry, Ron, and Hermione had more pressing matters to attend to (destroying the final Horcruxes to end Voldemort once and for all) than ask about Dumbledore's backstory. However, after teasing the conflict between the brothers and Grindelwald in that film, Fantastic Beasts: The Secrets of Dumbledore was the ideal time to explore this huge moment in more depth. When paired with the lack of screen time shared between Aberforth and Credence, this is now twice that the franchise has slighted and severely underused this character.