It's not wildly original - no. But you're totally wrong in calling it a 'blatant Rohmer rip-off.' It also 'rips off' Woody Allen's Manhattan and the early 60s New Wave films, specifically those of Truffaut and Godard. Thematically it is fairly original; Frances herself is a refreshing character, and considering Baumbach wears his influences on his sleeve, it's not really ripping off, but homage or pastiche. In a form which has now been around for 123(ish) years, to be truly original is near impossible. Post-modernism demands pastiche of its decaying art forms; Frances Ha is just a part of this trend. It's not that it's unoriginal but that everything these days is, in a sense, unoriginal.

you will come to realize that a huge part of any artist's work is filtering their ideas through the techniques/approach/language of their inspirations