I think we basically agree in the end, then, since everything you said is near exactly what I was trying to get across, just in slightly different language. Just with the additional bit that a lot of the time when someone in fandom is talking about the canonicity of something, about if something is in canon or not (in the fandom sense), they're basically doing that same sort of play. There's no stress intended behind questions like that a lot of the time, they're just doing that in a different manner but with the same intentions. Weighing out the default perspective, finding the starting point to start building their personal canon from.
I think in the end this was one of those "two different positions that aren't actually different after all, merely miscommunicated" situations, since you all but plucked my intended meaning right out from my head in that post.