Keystones: Almost Every One Needs to be Tied to a Cool Down

This is due to the fact that innate, passive Keystones tend to end up feeling underpowered or overpowered OR underwhelming. Not only this, but it has much less balance levers than a Keystone with a cool down. This is the current problem with most of the Keystones to where the hidden, innate power a lot of them provide can feel rather underwhelming, even if maybe they are OP. Heck, maybe Bond of Stone is secretly having the most impact on the game of all of them BUT WHO WOULD KNOW? Point is, all Keystones should be a slightly more powerful effect tied to a cool down. For example:

Grasp of the Undying Your next basic attack against an enemy champion deals bonus magic damage equal to 10% of your max health and healing you for 5% of your max health. (Halved in effectiveness for ranged champions) The cool down of this effect is reduced by 1.5 seconds (0.75 seconds for ranged basic attacks) every time you deal damage with a basic attack/spell to an enemy champion (max one reduction per spell cast). (25-20 second cool down)

Instantly feel the increased power? Yes, but the difference is it can only happen every 15 seconds compared to once every 4 seconds potentially. Another example:

Bond of Stone When a nearby ally takes damage that would put them below 30% max health, they are granted a shield equal to 14% of your max health or 9% of your mana pool for 5 seconds, whichever one is greater. The same target cannot be affected by an instance of Bond of Stone more than once every 12 seconds. (45-30 second cool down)

DOESN'T THAT FEEL BETTER!? Yes, a cool down based Keystone instead of just some hidden passive only you really notice feels much better.