Wow!
I was just in the Natural History museum in NY City - the theory with the short-armed dinosaurs (along with many other theories) - is that they were carrion eaters, not hunters.
Well, once they hunted them they became carrion................
I believe it has been reported that T Rex had a very large well developed space in the skull indicating excellent smell ability. I think I read about the capacity to smell rotting carrion that was 20 miles away. Also the long legs enabled rapid travel to a dead body.
Interesting theory ... how long are the arms on sharks, crocodiles, komodo dragons, or snakes? You just have to be faster than your prey. I'm sure they ate carrion too, but outside of vultures, I can't think of anything that is a pure carrion eater.