Ya know, I've thought of Cordy as A LOT of different things over the years, but I've almost NEVER thought of her as any kind of "damsel in distress." Or not the kind that you are implying, anyway. Not even on Buffy, because in my opinion, she's always been strong, charismatic, and often times stubborn as all get out and I think that's part of why I love her so much.
Yeah, she was scared and a little oblivious to the whole "things that go bump in the night" but I feel like that's more in part due to the writing, than Cordy herself actually. I'm sure there are people lining up to argue with me and to counter just about everything I've said thus far, let me just remind you once more, it's just *my* humble opinion okay.
Also, it's not necessarily that they change her character, but it's more like StarSlayer was pointing out - she grows as a person and gets more depth and layers added. It's really a beautiful thing to watch, if you like the character. Some do and some don't, it's fine. But I definitely wouldn't let those who don't like the character or her growth, steer you away from watching. Just...see for yourself BEFORE you make any decisions.
In short, I love this character as she's my very FAVORITE character in Whedonverse in general, and I'm always going to write love letters about her to anyone who's willing to listen. You don't have to my word or anyone else's into consideration for that matter, because all YOU need to do is watch it for YOURSELF and then YOU'LL see whether or not YOU like it. You don't need anyone else to tell you that you will or you won't. 🙂