they are not as strong as you think you just need tribe mate whit armor (recomendet is metal but chitin is ok)and shield and while he distracts the rex you can knock him out whith crosbow but it only works on lover lvl rexes i think the highest you can use this method on is lvl 50 but if you have more teamates you can do it on higher lvls
its good for geting rexes early whitout wasting lot of resources ( also bear traps help if your friend needs to change armor or shield)
If you use the bear trap strategy which is if you lead it into a Dino gateway that is shaped in a triangle and with a bear trap in the middle (Large Beartrap) and when it is stuck you must put a dinogate behind it to trap it and then knock out.
Pretty easy to tame as long as you are prepared. Always bring extra tranqs and narcotics to be on the safe side just because it takes a lot to bring them down. Upgraded rifles and crossbows are a godsend and make it even easier too. Get a Pteranodon or Argentavis, find a cliff/high ground where the Rex can’t get you and make it rain with darts and arrows. And when they start to flee once their torpor increases, run it down and don’t let up. I don’t make/use traps but this tactic works well for me. The giant murder lizard will be yours soon enough! Happy hunting and good luck!