What if Seeker's Armguard gave more Armor in response to enemy mobilty rather than farming?

I mean, it's supposed to be an answer to assassins, who basically all use dashes or blinks to get onto you. It kinda doesn't do this very well, though, since you're not getting the full benefit of your purchase until you get 30 CS after buying it.

I don't know, not getting the full value of the item you bought specifically to survive lane right away feels bad on paper.

Kinetic Armguard

Amplifying Tome (435) + Cloth Armor x2 (600) + 165 = 1200

+35 Ability Power +30 Armor

Unique Passive: Whenever an enemy champion performs a dash or blink near you, gain +10 Armor for 2.5 seconds. Subsequent enemy dashes or blinks refresh the bonus.

Particularly effective against foes who are especially dash-happy, such as everyone's pal .

Do whatever with the numbers, I just wanted to throw out the idea.