I tamed a level 30 carno everything went fine until a level 30 wild Rex came in my base my carno took it on and won saving my butt. Leveling up melee damage and health as well as stamina to do this. Note: My carno had 175 melee and 1300 health.
Tamed carnos are excellent almost all around: their health, attack speed, and base damage allow you to take on most of the creatures on the island, including Rexes and Alpha Raptors. Having a mated pair greatly strengthens this quality. They run fairly fast and can carry a lot, making great transport mounts. They are a fairly good harvester of meat and prime meat.
Their only real disadvantage is a slow stamina regen, even when stood completely still.