Please consider the context of the question. An artificial intelligence only needs to have the cognitive abilities of a random average human in order to be "AGI".

The average human has never published a bestselling book. A person who has published a bestselling book is an above-average writer. And, therefore, an artificial intelligence capable of writing a bestselling book would be above an average human at the task of writing books. Therefore, somewhere beyond an AGI.

Attempting to redefine AGI to "being better than most humans at most tasks" is moving the goalposts towards artificial superintelligence.