An argument does not have to controversial: it just refers to someone taking a stand, arguing for or against something. It does not have to be in opposition to other people's ideas either.
So now we have two options left:
writing that takes a specific perspective
and
writing to explain a writers ideas on a topic
I find both of them not perfect: I would rather say that an argument is a claim, or a statement, that needs to be supported. But from the two I think the better one is writing to explain a writers ideas on a topic (this is the best answer I think) since a perspective can mean a "point of view" and this not what an argument is.
