He has low value in round 3, because it can spawn only frost. aeromancer is beter in round 3 because can spawn thunder.
Carantir should have at least 2 options: spawn frost or spawn a boulder
Caranthir is one of my favourite characters and sometimes when i m bored i like to play wild hunt deck. He is good in certain situations and i think he is ok. In r3 if you have caranthir you should mulligan it away.