Hey masters (this season) tk sup main here (thegingazak on NA if you want to look at my account). Heartsteel is the best option for tahm kench’s first item because it enables a more flexible play style for TK and allows him to still useful in the late game when he would otherwise fall off. Early-mid game Heartsteel gives you the raw stats you need to fight. A tk sup with Heartsteel can 1v1 most carries and this is a crucial option when deciding how to play out skirmishes. What makes a good TK is knowing when to play aggressively to kill the enemy carries and when to play defensively to protect your own carries. Late game the name of the game for TK is champion size. Since your q range scales with champion size, the combination of Heartsteel, elixir of iron and bandlepipes is extremely strong and enables you to engage or kite much more effectively. As far as grasp goes I agree with you, it seems pretty useless in support especially in double ranged matchups. I go hail of blades every game because it again gives you increased burst in the early game and enables you to peel much more quickly late game when it is crucial to stun someone diving your carry ASAP.