I've never actually thought about this, but I suppose it could be a type of creative writing! Even though most of the 'creative stuff' has been already done by the original author, the FanFic writer still creates new scenarios and even OCs.

I think it depends but still counts. I've read some awesome extended universe in my day, and that's basically published fanfiction.

You're still creating new plots and with au's new situations and pairings even different endings (cause sometimes we hated the original ending). That takes a lot of creativity.

Of course!

I've read so many fics that were better stories than actual books I've read.

And AU's in particular, so creative. Yes you're borrowing certain characters but the story itself (and sometimes the entire world in said story) is brand new!

^ This.