The Rex good at:

-Tank

-Prime meat Collector

-causing other low level dino to poop when roar (only heard, not seen it with my very eye yet)

-wipeing dino life

But Rex bad at:

-Small attack radius which mean other creature can hit it from the side or back without you hitting them

-have hard time trying to turn around

-Can swim but lose oxygen while doing it

That all i know for know

Because rexes are slow, you can keep up with it and knock it out when it fleeing so they are easy to tame

Easiest way to find them is in snow biome on the island map, i found alot of them there