Question

What is the difference between scholarly, professional and opinion writing?

Answer 1

One is journalistic and valid but of different and varying opinions. The other is scholarly and emanating from Journals of various Academic impacts so voice might vary.

Answer 2

Scholarly journals are juried (peer reviewed), and journals allow no advertising, so there should in theory be little or no personal bias--just the presentation of research.

Opinion pieces may be of whatever quality, but writers may editorialize according to the policies of their media outlet, whatever it is--their own blog, or the New York Times.

Not sure what type of professional writing you mean.