The quest reward for ancient coin gives you the ability to level up one of your abilities(keep in mind this is not a champion level up so you don't get other stats like you normally do). At first it might sound decent on paper, but when you play supports who usually builds ancient coin(Janna and Soraka primarly), you will often have maxed your primary spell by the time you have completed the quest, which is E on Janna and W on Soraka. That means leveling up your other skills will not make you much stronger/usefull.
If you compare this quest reward to the one from relic shield and spelltheif it is really a lackluster. A 300 shield that regenerates out of combat and 50% movement speed buff every time you hit a spell is insanely more powerful and more reliable than having 40 more damage on soraka.
Another thing I noticed is you can't level up your ultimate unless you are level 6,11,16. This means the quest reward only affect QWE, and not R whatsoever. So if you are level 15 and want to use your quest reward to get your last level on your ultimate, it won't work. You just level up faster than you normally do, which means after you hit level 17 you won't get any stronger, it stops there. Meanwhile the other 2 support items will be usefull from the moment the quest is completed to the end of game. The health regeneration from ancient coin was also removed, which was very important on these passive champions.
**A way to improve this quest reward is to grant players the ability to level up a skill that is already maxed. Ex: a fully maxed level 5 soraka W heals for 200. With this quest reward you can break the limit and level up to 6, so she will heal for 230(since she usually get 30 heal per level up). You will also have the important decision to choose which skill you want to level up to 6, depending on your playstyle and ingame state.**
I have seen Soraka and Janna players go spelltheif, but never have I seen Zyra go ancient coin(for obvious reasons). With this change people will probably pick up the ancient coin so we can see some variety in champion build. This will truly make this quest reward unique, appealing, and more rewarding, comparable to relic shield's and spelltheif's quest reward.