Yes, TK has always been OP since release.
Whether it's the % of his bonus health passive as magic damage from his R, his double free health on his E (combined making health stacking WAY too efficient on him, then add in Titanic Hydra...), or the fact that he can swallow allies to save them from literally anything (oh, you just landed a really difficult to land stun on my squishy? Nom-nom-nom), or the fact that his 2 second 70% slow is only on a 6 second base cooldown (so 3.6 seconds if max CDR).
He's way overtuned.
To start getting him balanced:
Slow cooldown increased (to 8 seconds probably, or to 10/9/8/7/6).
Reduce how much gray health he gets (perhaps 1/2 or 2/3 instead of all damage taken).
Change/Lower the bonus magic damage on his ult to 20/30/40 + 2%/3.5%/5% of his bonus health.
At least if you start this way, you can give him power where he is unique (in his swallowing an ally / enemy, and his 2 man semi-teleport). There's no reason to make him simultaneously a ridiculously strong tank, duelist, and peeler.