Actually, 7th is correct.
All BB arcades and alternate story endings are canon and actually happened.
But Amaterasu made the timelines start over until something different actually happened(Nu going into Cauldron by herself, Ragna beating Hazama.)
But since Amaterasu is destroyed, there are no more timeloops so if there are alternate endings and arcades in BB3, then those will probably be not canon.
True, true. Though I expect one thing they could do is have all of the "true ends" lead up to everyone meeting or something - akin to how some of "true ends" in stories in CS seem like they COULD, in theory, match up. Not all of them do, obviously, but it's probably how they're going to do BB3, then the "alternate paths" and "continuum shift" mess'll just get turned into typical bad ends, I expect.
The thing about these other worlds though: Takagamaha-- whatever they were called, they COULDN'T have been destroyed unless Hazama had seen every single possibility out there
. There are probably millions more "canons" out there, and in Hazama's mind, he actually has experienced and lived through every one, even if they were reset/pushed aside for the "true" one.
And... "Only two timelines matter"? That's not necessarily true. I mean, we have quite a few characters that remember a lot of them. Rachel, Hakumen, Hazama-- Etcetera.