Is Helen Fielding really middlebrow though? Sure, not massively complicated in plot, and definitely not difficult to read. But her themes really speak to a generation of women, she said some really interesting and quite complicated things about society, our expectations of women, and how we live now, and I'd say definitely not a trashy book.
She draws on the themes of great literature that came before her: Pride and Prejudice being a really obvious example - I mean, the entire Darcy
Bridget and whatsisname triangle is basically commentary on Austen.
And what's not obvious to those who haven't read it (and you should because it's a masterpiece) is that stylistically, it's a loving homage to a much earlier 20th century classic, The Diary of a Provincial Lady. Which is an absolute gem of a novel, and perfectly and cuttingly captures the interwar/WW2 period.
I think the only reason Bridget Jones is slated and underrated is that it's women's fiction, written for women, dealing with themes and problems of being a woman. If Martin Fucking Amis had written it the bookish intelligentsia would be fawning over it.
In short, Bridget Jones is a really important 20th century novel. Whether you enjoyed it or not. I don't think it's middlebrow at all.
(And if we want to talk novelists who were considered middlebrow in their day, in the sense that they were aimed at and enjoyed by a huge and wide ranging readership and wrote with the intention of making money as well as making art, then may I present to you one Mr Charles Dickens. Also Mses Bronte, various, and Jane Austen herself.)