My take is somewhat the reverse of that. Both are cannon.
The author (if he/she is alive) generally does have a say in it.
A collaborative effort can produce better results than a single effort. (more mass appeal) Two minds are better than one.
Even written books have editors.
Now the manga is probably also a collaborative effort, but an anime costs more to produce so i'm thinking there is a larger focus on mass appeal.
mass appeal -> more people who watch get to know it.
people who write and read fan fics are percentages of people who know it. (+ people who write read fanfics without general knowledge of cannon)
So for most fanfic writers and readers anime is more cannon than the manga is.
The author (if he/she is alive) generally does have a say in it.
A collaborative effort can produce better results than a single effort. (more mass appeal) Two minds are better than one.
Even written books have editors.
Now the manga is probably also a collaborative effort, but an anime costs more to produce so i'm thinking there is a larger focus on mass appeal.
mass appeal -> more people who watch get to know it.
people who write and read fan fics are percentages of people who know it. (+ people who write read fanfics without general knowledge of cannon)
So for most fanfic writers and readers anime is more cannon than the manga is.