Ancient Coin's quest reward is too weak, not just the coin drops

In an average game, you'll probably be finishing the quest around level 8~9. And it may benefit you for a short while to have that second skill rank in ultimate at level 10. But the champions who build it are Soraka, Janna, and Rakan. None of which get a significant spike in power at level 11 since their power comes from the actives and passives on the support items they buy.

Meanwhile, mage supports get a speed boost to reposition for better shots. And tank supports get a shield that is stronger at level 1 than Rakan's is at level 18 (while despite his extremely short AA range he can't buy Relic effectively because he's technically ranged.)

And either could replace their quints with Exp. to get an even better effect than just a skill point. Since they'd also be getting their normal bonuses to defenses and AD from an actual level up.

Ancient Coin needs a different reward for its quest. My suggestion is either a permanent speed boost towards low-hp allies (like Soraka's passive) or something like True Healing, where their heals on allies ignore 10% of the penalty from grievous wounds.