What do you guys think? Do you think that the author should have the most control over a fanfic? Or does someone who grants the usage of a character automatically gain control over the story?
Personally, I think that the author should still have the most control. The story is their idea, after all. All a person who gives permission to use a character (or idea) gets to control is what they granted permission for. And even then, in the end, it's the author who has the final say and if they want, they can remove that character/idea entirely from the story.
Just because someone gives permission to use someone or something in the story doesn't automatically elevate them above the author as the controller of the fanfiction. Sure someone might think "Well I gave them the privilege to use my character/idea so they should do it how I want!", but it is the author writing the story, not that other person, and if that person becomes too much of a problem, their idea/character can be utterly removed from the story.