It’s really not that hard a tame. Trap it with stone gateways and a bear trap. Knock it out with maybe over 100 tranq arrows. (Which aren’t as hard to get as you may think). And BOOM! You have your self a rex. Oh yeah and feed it some kibble, for best taming better stats AND less time for taming. I would say it’s a medium tame.
Dont be scared of them, get a flyer and make sure to have a high health and stamina, fly at him (make sure its only one or your dunso) and let him take a bite of your flyer once in a while then lead him into a square wall of dino gates with a trap in it. Once he is stuck quickly close up the open gate, laugh at him and shoot him (alot)
Okay so people are saying to use platform saddles which yes is not bad it’s just work to get a quetzal, if you have 2 people all you have to do is build 3 stone Dino gates in an unfinished square away from the Rex, then get the Rex to aggro on you and lead it in and go through the middle square (you can use large bear traps but I never use them) and then while the Rex is still aggro at you the second person needs to come behind and place the last gate.