The placement of Tears of the Kingdom and its predecessor in the Hyrule lore remains a mystery, despite the established timeline of older Legend of Zelda titles in the Hyrule Historia. Breath of the Wild's time travel and changes to the ancient past have redefined the end of the timeline, leading to increasing cryptic statements from Nintendo about the current state of the Zelda timeline. The newly discovered Depths beneath Hyrule and the focus of the story seem to separate this new era of Zelda's timeline from the previous ones.
References in Hyrule's Depths
Most of the equipment from past Zelda games, like Ocarina of Time's armor set, can be found in the depths rather than hidden across shrines or EX chests like in Breath of the Wild. While not all armor or weapons from previous games are located underground, many of them can be found in ancient Zonai chests, implying that these gear sets are from an even older past before the founding of Hyrule. While referencing older games may not be definitive proof of canon, it is a common theme in Tears of the Kingdom's armor sets. The connection to the Depths, Zonai, and the founding of Hyrule makes finding gear from previous games down there particularly significant for the larger timeline.
Founding a Surface Hyrule
The timeline in Tears of the Kingdom doesn't align with older games in the series, particularly with the events in ancient Hyrule involving the kingdom's founding by King Rauru and Queen Sonia. This contradicts the established timeline of Skyward Sword, where Hylians lived on Skyloft before coming down to the surface. While it's possible to hand-wave this inconsistency by suggesting that the Hylians returned to Skyloft before coming back down, this doesn't seem to be the case in Tears of the Kingdom's Sky Islands. Additionally, reconciling the history of Hyrule still leaves an issue with the timeline of Ganondorf and Demon King Demise, who weren't defeated and reincarnated until after Skyward Sword. As such, the founding of Hyrule alongside the rise of Ganondorf as the Demon King creates a new continuity for the series' heroes and villains.
Tears of the Kingdom is a Reset, Not a Continuation