"With very few notable exceptions (e.g. Bronte, Austen, Shelley, Eliot) there were virtually no popular women's authors until the latter half of the 20th century, whether you're going back as far as Mallory or as recently as Fitzgerald, Steinbeck and Hemingway. If you like literature before say, 1950s or even 1960s, you're almost certainly looking at a male author"
Without wishing to criticise you, that's very much not the case - the issue seems to be rather more subtle than that. There has been a high proportion of women writing professionally (i.e. for money) since at least the late 17th century, whether they chose to write anonymously, anonymously but acknowledging that they were female, pseudonymously (with both male and female pseudonyms),etc. (There may also have been male writers claiming to be female.) For example, Eliza Haywood, a professional writer in the 18th century, managed to write over 70 works, from political satire to drama. Her best novel, I'd say (available in Oxford World's Classics) is The History of Miss Betsy Thoughtless - the story of an unhappy marriage, and well worth reading today. Her potboilers include unforgettable titles like "Love in a Madhouse" (sadly not reprinted, I think).
However, it does appear that women authors tended to write in genres which were seen at the time as populist - as 'chick-lit' is now - and thus were less respected as authors then, and as a result of this among other factors, tended not to be incorporated into the canon of English writers. Novels, for example, were not necessarily well regarded during the 18th and 19th centuries.
If you look at contemporary writers and reviewers, you'll find "exceptional" writers like Austen listed alongside others who are now forgotten, both male and female. However, a lot of these 'forgotten' writers (both male and female) are being reprinted, and I recommend looking them out. It just needs a TV adaptation or two to make some of these writers household names.
For anyone interested, here's a few choice recommendations for novels by women authors who are less well known than they might be - all the books are out in Oxford World's Classics.
Belinda (Maria Edgeworth) - a great read, very much setting the scene for Jane Austen in its depiction of a young woman making her choices in the world, although you may doubt whether you can actually get breast cancer from dressing up as a man (okay, maybe Edgeworth doesn't believe you can either). I like it so much I'd name a daughter Belinda.
Hester (Margaret Oliphant) - the struggle between an old businesswoman and Hester, the penniless young girl. Definitely good.
The Wanderer (Frances Burney) - a simultaneously idiotic and gripping story of a refugee from the French Revolution. Very powerful depiction of what it's like to arrive in a strange country with no friends and no money. (But with the additional complication of not being able to tell anyone your true name, and being too honest to conceal this fact, thus pissing your benefactors off, which manages to extend the novel to about 800 pages).