Suggestion: A simple way in making Assassins more manageable

Thunderlord's Decree has always been a "go to" keystone as of late, regardless of who you pick. But for champions like:

Is it really necessary? Especially with the inclusion of Duskblade, and the wide variety of items that AD champions have to choose from? In short, what if Thunderlord's decree took the Warmog's method?

Reminder

Grants WARMOG'S HEART if you have at least 3000 maximum health. UNIQUE – WARMOG'S HEART: Regenerate 「 1.5% maximum health every half-second 」if damage has not been taken in the last 8 seconds.

In other words, what if there was a prerequisite before the player can take full advantage of Thunderlord's, just like how there is for tanks when buying Warmog's? This requirement could be building a certain amount of AP for example? It doesn't have to be a huge amount, perhaps a more rounded number like 100 AP, that's if it's going to be something that comes into it's own later on, like Warlord's Bloodlust.

Right now, the amount of items available to AD is much wider compared to AP, which means that most Mages build the same items. Having this keystone more exclusive to the Mages could make some of the AD assassins a little less annoying.

Is it going to solve every problem with Assassins? Probably not. In fact, it might not solve anything, especially without testing.