Hrm, honestly? On the matter of Castle, she's actually very far off the mark. S1 was iffier, but season two has been exceptional on Beckett. Particularly in terms of Beckett and how Castle views her. The show is very, very good about displaying Kate's competence and the fact that Castle adores that about her.

As for genderswap, for me it's a lot about exploring how that character would work as a woman. For example, in Trek I ADORE Uhura as is, Chapel, etc, but let's take Spock as an example. A lot of the time, when I genderbend him, I'm trying to explore how Vulcan being matriarchal would affect him. In such a case, it wouldn't make much sense to use say Christine or Nyota in the role. The change required there would be so massive as I'd lose their voice in it. At least, I feel that I would. I'd rather feature them in the story as themselves than do that.

Erasing established female characters from the narrative is a worry. Battlestar Galactica did that with Starbuck. With Kara filling the 'daughter' role for Commander Adama, his actual daughter vanished into the ether and her name was given to a Cylon. Which, eh, no.