I think that's a good point. Ts usually make such statements as a way to show they are listening and to verify that they are understanding the clients point. So if the T mirrors back a statement that shows they completely miss the point then I wouldn't hesitate to tell them. I have done this many times and it's always helpful, and as a T I'd hope clients would do the same. Even if the session is only to vent, I want them to get the point of what I'm venting about.