Northanger Abbey was actually one of Austen's first completed novels, and she submitted it in 1803. [By contrast, Sense & Sensibility came out in 1813] However the publisher held on to it for about a decade, until Austen's brother bought it back in about 1816. Austen then spent some time revising it. Cathy's name was originally Susan, for one. How dedicated she was to revising it isn't really known [at least not to me]. She was already ill, and she died about a year or so after her brother got it back for her. He had NA and Persuasion published posthumously as a set.

I love Northanger Abbey, but I understand what you mean. I suspect it was just the growing pains of Austen working out how she wanted her novels to be, and then she wasn't able to spend enough time revising it when she had the chance.