Proposed Darius change

So, Darius is a bit strong right now, so I thought about 1 way to change him to reduce his power a bit. Make it so that his E's passive %armor penetration now only applies to units he pulls with his E, for 5-7 seconds. This would reduce some of his hidden power in laning with only auto's and his Q, without using his E. And if he does use it, it won't change much, but now the cooldown is down and he's used some mana to get a bit more damage off.

This may not be the best change, but it's just an idea I had.