1. The amiibo outfits match the text style of the in-game, not-amiibo BotW outfit of the same style. They are also worded in-character for the games, not out of character. Considering we never got a ruling on whether or not they are canon, the fact they provide setting details suggests they are.
The Palace of the Four Sword has similar flavour text saying that it was built for heroes, but due to it giving us a different ending, not being acknowledged in HH, and not making sense from a chronological perspective, we know that that's not canon.
Ancient Stone Tablets is an obvious ingame sequel to ALttP, which is a canon game, but AST itself is not canon as mentioned by HH, despite AST treating the events of ALttP as canon in its story.
Historical cultures that had mythology-as-history setups similar to Hyrule also had people who lived at the same time the legends were common that wrote down that the legends were not considered entirely factual in their own societies, but more allegorical accountings of history.
But we, the players, know that to not be the case. We've played OoT, and those legends had to come from somewhere. It makes sense to assume they're true until proven otherwise.
If the amiibo outfits are canon and BotW is part of only one timeline, then you'd have to answer that question as to how they knew the history of all three timelines since the amiibo outfits represent games from all three timelines. In order to justify them not at least knowing about other timelines, you either have to merge the timelines or start removing parts of the game as being canon. And, frankly, we're assuming the wishmaker wouldn't simply end up finding out from the Triforce itself if they bothered to ask. Why they would ask, how they would know to ask, or even what question would lead to such an answer is far too massive of a topic to explore; there's too many possible answers. And that's assuming Hyrulians didn't find out through some other method we're just not aware of or simply didn't know they existed from the very beginning; given they know time travel is real and in at least one timeline that alternate versions of Hyrule exist, it wouldn't be much of a stretch for them to figure out that other timelines exist or for someone to be dumb enough to think merging them is a good idea (maybe Ganon did it to gain more power? Seems like something dumb he'd try, and it would explain Calamity Ganon).
Sorry, far too many ifs, maybes, hypotheticals, and overall fanfic for me to accept this as a valid argument.
