It's a day ending in 'Y', thus Blizzard is having to navigate some balancing problems in Diablo 4. In this instance, though, the devs have made the rare choice of just embracing what's going on, maintaining an unintended change from the Hellfire Torch in Season 15.
The Hellfire Torch is a new Unique Charm that came with the current season. Between serving as a Set Charm and a number of powerful bonuses, it's a particularly worthwhile bit of equipment that was even better than Blizzard bargained for.
In execution, players found they could get the bonuses of having three Unique Charms and a complete five-set of them at once through the Sea of the Golden Epiphany and the Seal of the Diamond Mind. This has rippled through the community pretty heavily, leading it to be a dominant force in the action-RPG's landscape. As such, players have been quick to feed this back to Blizzard, who're just rolling with it for now.
"While we've confirmed that this interaction is resulting in behavior beyond what was originally intended, we’ve decided not to make changes to it during the current season," Dan Tanguay, design director on Diablo 4, says on the official forums in a statement published by Rich 'Filthierich' Bantegui, a senior community manager for the Diablo series.
"We know many players have spent significant time earning the Hellfire Torch and building characters around it," he continues. "Because of that, we want to be thoughtful about making adjustments mid-season that could disrupt those investments."
It reads to me like the solutions right now involve either damaging people's builds in a way the devs dislike, or causing further disruption in a flailing house of cards sort of way. Tanguay asserts this will change, just not for the time-being.
"We’d like additional time to investigate the underlying issue and ensure that any future changes are implemented correctly and behave as intended," he says. While this may be frustrating, the acknowledgement demonstrates complaints haven't gone unheard. While you wait for a patch, see if the Hellfire Torch has any other quirks you're unaware of.
