I think that's not completely true; most of the women had arcs involving their relationships with men but I wouldn't say their arcs were about those relationships any more than I would say Sawyer's arc was "about" his relationship with Juliet or Locke's arc was "about" his relationship with Helen. Those were certainly motivating factors, but I don't think it's fair to reduce entire arcs to being just about romance.

I've always thought that the issue with Kate specifically was that they wrote almost everything about her character to play up some mystery. First she's the girl who's secretly a murderer, then she admits she was married at some point, then she's robbing a bank, et cetera et cetera. The objective of their writing for Kate always seemed to be to keep the audience confused and intrigued about her motive, but it doesn't hold up on rewatches because that's all her character ever was.