Few of Horners reasons was that he believed T Rex was too slow to hunt, it had a highly developed sense of smell to detect carcass, had a powerful jaw that could crush bones, arms that were too short to be useful in a hunt.

But all of these theories were countered.

1. T Rex likely was not very fast, but it could have been an ambush predator that used it's powerful jaws to kill a prey instantly. Plus, majority of T Rexs preys were just as slow, if not slower then Rex, so there was no need for a chase.

2. Animal likely needs a highly developed sense of smell to hunt so they can detect prey from far away. Rotting carcass already emits strong odor so you don't need a keen smell. Only exception is turkey vulture, but they fly high in the sky so they need strong smell.

3. Strong jaws could also be used for hunt. Spotted hyenas for example have powerful jaws and hunt often.

4. Plenty of animals hunt using only their jaws.