I agree to some extent. Rachel and Bruce shared a connection. It was a different kind of relationship from "movies" point of view. Many criticize this relationship because it didn't feel romantic enough. It was not meant to be. They were friends, they obviously liked each other and wanted something more, but they slowly fell apart.
There are a couple of nice moments in Begins. When Bruce arrives to Gotham, Rachel hears the news and is shocked. She moved on, but now she has hope for something more with Bruce, not sure how to manage all of that. And when Bruce encounters Rachel after his first playboy millionaire act, he wants her to see him as who he really is. He wants her to understand him because he has hope for them too.
Rachel Dawes: I never stopped thinking about you. About us. And when I heard you were back, I-I started to hope.
Bruce Wayne: [Rachel kisses Bruce]
Rachel Dawes: But then I found out about your mask.
Bruce Wayne: Batman's just a symbol, Rachel.
Rachel Dawes: [Rachel touches Bruce's face] No, *this* is your mask. Your real face is the one that criminals now fear. The man I loved - the man who vanished - he never came back at all. But maybe he's still out there, somewhere. Maybe some day, when Gotham no longer needs Batman, I'll see him again.
At the end of Begins, Rachel sees a new shade of Bruce's personality. She now knows that he is not some irresponsible playboy. He is noble, he has a purpose and a mission. She admires that, but I don't think she is sure she likes it. Now she has hope, the same hope Bruce has, at least for now. In TDK, Rachel has moved on. She found Harvey Dent someone who understands her, someone who share goals and interest, someone who loves her. But she still harbors feelings for Bruce.That's why she allows Bruce to kiss him in the apartment scene, thats why she hasn't told Harvey her response about marrying him. She is still not sure. That's her predicament in the movie. She has to make a choice.
As the film progresses, she realizes that Bruce and her have grown apart, that she doesn't want to follow Bruce into that path. When Dent takes the fall saying that he is Batman, Rachel is upset that Bruce didn't say anything. She cares for Harvey, whereas she doesn't understand Bruce. She chooses Harvey Dent, but she knows that Bruce would be deeply hurt by all of these. Then came the letter. It is a great thing with a beautiful, and at the same time sad message. She is hurt by all of these, she knows she gave Bruce hope for something that now she can't give to him. She is honest, and she still cares for Bruce by encouraging him to not lose faith in people. It was the most sensible thing for her to do, she couldn't handle it. And she knows that Bruce might lose his faith in her, she takes that chance.
It was a more complex thing than it appears.