When The Winchesters aired in October 2022, fans were taken to the earlier years of Supernatural's Winchester family lore due to the promise that was made. However, instead of making the legacy marked by the franchise large in scope, it appeared as though the spinoff only raised more questions. The jarring flaw two years post-cancellation has left a mark that still seems unresolved for the audience and continues to cause questions in the fandom.
The Supernatural fandom should blame Robbie Thompson and former actor Jensen Ackles, who produced the show. Starring Mary and John Winchester, The Winchesters focused on the younger versions of the characters. Where longtime fans awaited their backstory to be told, the execution was entirely different, going completely against the canon. This seems to be the most highly debated choice made in the entire saga.
Breaking canon with an alternate timeline

The major problem the fans had with The Winchesters is that the fandom of the saga had an issue with the inconsistent approach to the canon of Supernatural. The show served as a standalone prequel; however, it brought forth additional information and backstories that contradicted important aspects of the show.
For instance, Supernatural showed John Winchester to be aware of the secretive Men of Letters, which was a major discovery for his sons, Sam and Dean. Moreover, John also knew Mary was a hunter, which was hidden from the original timeline.
These contradictions will certainly make the fans question certain things. With the earlier approach of “no lore,” the show required some absurd twists to its story to make sense of its contradictions. When the show revealed it was set in a different timeline, some viewers were more baffled than relieved. Instead of providing clarity, this angle simply estranged the spin-off from its parent series.
The missed opportunity for a richer lore of Supernatural

While creating an alternate timeline, The Winchesters missed the chances to capitalize on the rich lore that made Supernatural great. The original series had no shortage of monsters, mysteries, and character arcs, yet the show chose not to focus on those. Instead, it came up with new conflicts like the Akrida, which did not resonate with viewers.
During the 15 seasons of the original series, the stakes increased steadily over battles with cosmic forces such as God himself. It was possible to view The Akrida as a comparable threat, but they lacked the rich, powerful, and ominous build-up essential to being truly menacing. Including them in the story only further distanced The Winchesters from the grounded, myth-heavy world that the fans wished to revisit.
A complicated legacy for John Winchester

Another point of debate was how The Winchesters showed John Winchester. In Supernatural, John came under fire for his parenting. He was described as obsessed and emotionally absent, especially towards Dean, capturing and fueling Dean's story arc throughout the series.
In contrast, The Winchesters softened John’s edges, portraying him as a charming young man with good intentions. While that worked for an inception tale, it clashed with what most fans understood. For some, this version glorified Supernatural’s otherwise traumatizing John Winchester—too complex for blanket treatment from people who revered the stories’ complexity.