KT is a good legendary no doubt but he is not super high tier. I've seen him in two types of decks in high ladder (rank 3+) that is Priest and control warrior. I didn't really like him in priest they don't run enough stick minions late game to get enough value from him. Control warrior on the other hand is the deck for KT. If I know at least 1 warrior deck in the latest HyperX invitational tournament that ran it. That was RDU and it went pretty well for him He won the hole thing
I have it in my control warrior deck as well and he really preforms. He is not on the level of Loatheb or grommash but he is better than onyxia or deathwing which probably would be the next legendary cards on queue in the warrior deck. So if your deck runs Rag, Class legendary, Alex, Sylvanis, Cairne, Loatheb you need to put KT in it.
He just adds a extra win condition you play cairne turn 7 and he lives turn 8 KT and trade Cairne and its almost 99% game. With the extra sticky minions like sludge belcher armorsmiths ect he will pull something. Just don't play him on a empty board. I've done plays like Alex and he plays rag it hits my belcher and on my turn I KT trade my alex in his rag, get my alex back and pretty much run the game.
People saying that he gets owned by Hex, polly is nr 1 not playing on the current ladder because nobody plays shaman or mage but if you feel he isn't getting value against SW: D or hunters mark or execute you are playing him wrong. As a rule If none of the players are on fatigue and you wont get benefit from his effect the same turn you play him... Don't play him. The idea is to play big threats over and over again until he runs out of remval for that 1 threat and instead responds with a counter threat then is when you play KT trade you minion into his minion and KT will return your minion. You should expect a instant SW: D and still be happy in how you played him imo.