Some scientists have been saying that for years. Considering the size of a T-rex it would not have been a great hunter and tangling with other dinosaurs even herbivores of equal size could result in a severe injury. I watched a neat CGI show about it once, basically a small group of carnivores like a T-rex would follow their prey closely. They would try to scare them so one would break its leg, or simply go after the weakest one in the heard. If you ever fell behind within the heard you were dead.
I have no doubt a large pack of raptors if they wanted to could take down a T-rex. It was a big, mean, but slow creature and not the ultimate bad ass as we would expect.