I told you all I would explain why Hyrule Warriors is canon in another chapter. This is one of the only instances where I agree with MatPat on a theory of his, because it's correct. Before I jump into why it's canon, let's see why people think it isn't.

Timeline mumbo jumbo. People believe that since Hyrule Warriors opens up gates to the past like how Marvel Endgame does, it's not possible to be canon. But, why not? Breaking it down, we can see the moments where it does and should make sense. The first time we travel through time is going back to the Hero of Time era, aka Ocarina of Time. We are introduced to Darunia and Ruto who have not died yet, and therefore have not awakened as Sages. We help defend the Temple of Water and thus Morpha is never a thing because Ganon isn't able to curse Lake Hylia. Problem solved, recruit them back to our time.

Twilight Princess era happens right after the end of the game. Zant has been resurrected by Cia, and she has also turned Midna back into her impish form. We help Midna, then go to her castle to take back the land. Thus ending that mission and recruiting her and Agitha to help in our time.

In the Skyward Sword era, everything happens way before Link is born. We meet Fi and she says Link isn't her master, but sort of still is. (It's because Hyrule Warriors Link is the hero of another time. The hero of Warriors, not of the Sky.) Volga catches Ghiarhim's attention and he gets involved in Skyloft. The Imprisoned is resurrected early with the help of Cia and the hero of Warriors slays it with the help of Fi. Ghirahim is banished and Fi joins our team. The hero of Warriors defeats Cia, but Ganondorf is resurrected and summons back Ghirahim and Zant for revenge. Ultimately they are defeated after Ganondorf absorbs the complete Triforce and becomes Ganon once again. Lana takes the mantle of Guardian of Time, deciding to watch over every Zelda game and not intervene from that point onward.

Before that happens, however, another anomaly occurs. Dark Cia opens more portals and summons the Wind Waker era, the era of the hero Keeps the Sword. This is the only possible way that the Rito enter Breath of the Wild. That aside, Lana helps Tetra and King of Red Lions find the real Cia and defeat Phantom Ganon. This all takes place right after Wind Waker, when Medli is awakened as a Sage and Zelda dresses as Tetra once again. Before she can go on the journey of Phantom Hourglass, this happens.

Let's talk about the Rito. The only place they appear is in the adult timeline, starting with Wind Waker. Then for some reason, they're in Breath of the Wild. Unless BOTW comes right after Spirit Tracks, the Rito shouldn't be there. Not in the presence of the Zora. See, the Rito are Zora but evolved because of the great flood. Both species can not exist at the same time. Hyrule Warriors had to happen because it's the only game that has Zora and Rito coming together to fight. Breath of the Wild doesn't explain how those two species exist together in that game.

Okay, so let's say Breath of the Wild is the game that connects all the timelines. That would make sense, right? Actually, no, and for a strange reason. Zelda has the complete Triforce. That's the power she has to awaken by connecting with her goddess side. The Triforce seals away Ganon, as seen time and time again. But, isn't Zelda supposed to just have the Triforce of Wisdom? How did she get all three? Unless Breath of the Wild 2 comes to explain it, the only possible way is from Hyrule Warriors. Ganon gathered all three pieces and successfully used them to shape Hyrule to how he pleased. That Triforce was separated for a brief time at the end, but then the Wind Waker era happens and it stays connected. Zelda inherits the essence of all three goddesses and is able to seal Ganon away when he's weakened in Breath of the Wild.

The map. Hyrule Warriors's map is very vast but very important. Before every fight, you see where the army is traveling based on the location from Hyrule Castle. This is the map from the Fallen Hero timeline. The only piece from that timeline. Let me explain.

Hyrule Warriors technically is the last game of the Fallen Hero timeline, but then it pulls characters and events to it from the other two timelines, like the Zora, Rito, and Twili. That's how all of the timelines merge together. At the end of Adventure of Link (the game right before Hyrule Warriors), Ganon's soul is shattered and Link puts the Master Sword away, letting it guard part of his soul. What happens in Hyrule Warriors? The pieces of Ganon's soul returns, one of which was guarded by the Master Sword. The Fallen Hero timeline is so important, and to prove that Hyrule Warriors is canon all you have to do is look at the map.

There is one more piece to help prove this game is canon. Why do the Champions in Breath of the Wild wear that unique blue color? Shouldn't they wear the hero's green? Look at the scarf Link wears in Hyrule Warriors, and there's your answer. It was the game that came right before this, after all, and they commemorate it by wearing his blue color. They even put the Hyrule Warriors outfit in Age of Calamity!

So it goes: Adventure of Link -> Hyrule Warriors (merging with the other two timelines) -> Age of Calamity. If AOC succeeds, that makes a new timeline, but if it fails then you go to Breath of the Wild and then BOTW 2.

The Rito, the map, the Triforce, and the scarf all help it make sense. I believe that Hyrule Warriors is canon to the Zelda timeline and I'm probably the only one who does.