The word "canon" has changed quite a bit over the years and has many meanings now, one of which is authentic work by the original author (or chose successor)
That is the definition we use must use when describing fictional stories.
Why is the person who made the story the only person we should trust as having the actual story in mind?
I dunno, maybe because they made the story in the first place.
It's theirs. Not anyone else's. Anyone else's alterations do not matter, the original is the only authentic one in regards to the story.
Everything that goes against that original work or addition made by the original author is by definition not in continuity with said work, and should be discarded.
Wanna know why GT can't work anymore? The depiction of Hell alone renders it out of continuity with the authentic story because Akira Toriyama made the Hell that exists in-continuity .
So any depiction of Hell that is not in line with it must be discarded as no longer in continuity, and not part of the story.
This includes all Filler depictions of Hell.
It was recently stated they never encountered a Legendary Super Saiyan before, so Broly is no longer in continuity.