“With those tiny little arms I think the T. Rex were scavengers.”
There would be no need for jaws like that to pick up already dead animals lying on the ground. And with jaws like that, as with snakes, it would not need large arms.
Sharks don’t need arms either. They just swim up and take a bite. If T-Rex had any kind of sprinting ability it would have made for an ambush predator against very large herbivores. But as with most meat-eaters they swing between predator and scavenger.
Dead dinosaurs have awfully big bones with lots of tasty stuff inside just waiting to get eaten. Big powerful jaws made those bones into good eating .
Eagles aren’t scavengers and they don’t have arms. There were herds of short legged, fat gravers that were popping out of clutches of 50 eggs at a time and with double the foliage density of today (CO2 was over 2X) and 50% more oxygen, the plant eaters grew muscle fast.