Huge Tolkien fan here. But the list of great authors and great books is long. It is certainly not unfair to compare Nabokov, Rushdie, Kingsolver, Ferrante, etc etc etc to Tolkien. Some were linguists, translators, literature professors. Some were journalists. Some had no obvious qualifications at all. Some wrote their novels very quickly, some took decades. Shakespeare and Dickens were not linguists and (mostly) wrote very quickly.