I suppose I should clarify on things a bit.
firstly I consider anything not established within the source material, but that is widely accepted as an aspect of the universe or at least a repeated idea within the fandom that is not necessarily an aspect of the story. My opinion of the fact of what constitutes canon is all information one could learn from the official released material on said universe. (meaning any other stories linked to it.)
I doubt you'd change your own position, as most of the matters of whether or not it's ok to utilize fanon which we disagree off are obviously purely a difference in taste, so I'd rather just agree to disagree. Im merely stating that not all fanon is the same, you need to take it on a case by case basis whether or not you agree with this is your business. At the end of the day.
I can tell you right now with very reasonable certainty that what you did was have characters act like they were in a story with Takahashi's average tone but having the story treat the characters like they weren't. Takahashi herself would tone down characters actions in more serious scenes, so you need to do that.
I don't particularly care how Takahashi writes, I'm a completely different individual with a different writing style, and I consider myself a fan of her work because of the ideas and characters in them, which I do strive to portray accurately. The idea I need to also follow her writing style is silly, because if I wanted to read "more takahashi" I'd simply go read one of her other manga.
Now onto the dumbledore thing. I dont consider it canon because it was not in the books, I do get that about history however I'd say it's silly to, after years following the conclusion of the story you suddenly drop things like that, outside of a followup story or the like and not within any actual stories or the like within the continuity then it's still not quite canon.
I dont have a problem with him being gay, nor does it have to be announced every two seconds or the like but it isnt IN any of the original material. My policy on if something is considered canon is that if I could read through all original source material, without reading anything about it outside the actual story, and any that are within the same universe and said fact, such as Dumbledore being gay isnt at all established in any of that then it can't very well be considered canon. Id also say that the comment on "confirmed bachelors"
I have no problem with him being gay, but it's not in any of the actual material, so it cant be considered canon. I also dont think you need to shove it into people's faces, but what does him being gay actually change about the character? What does it change about any of the actions he takes in the story?There is no way that one would be able to glean his sexuality based on all knowledge of his history, nor any of the original source material.
At the end of the day, it's not something anyone would be able to know purely from the story so I dont feel it can be considered canon. I do understand others may have different opinions, but i follow the belief that a story needs to stand or fall on it's own, and that applies to any aspects of that story.
I'm not gonna hold it against people whether they decide if he is or isn't gay, because fandom has been ignoring sexuality since the dawn of time, especially when said sexually isnt directly established in the source material.
Id also say that people are going to write what they want, sometimes using fanon works, and sometimes it makes the characters and stories less interesting. The issue with the statement you are making is that something being interesting is subjective to what you find interesting. I dont particularly think it matters, I'll just read the stories I find interesting, and avoid the ones I don't. I think you're taking this stuff a bit too seriously is all. And Id also say that often times it's merely an issue of how people interpret characters, I strive to portray all the characters I use accurately, but Im not going to go all Stazi on somebody if they dont want to put in the same level of effort to keep to the canon.