Last Whisper is too efficient against non Tanks. It should apply to bonus armor.

is a must buy on certain champs, because late game everyone has so much base armor that it is always efficient.

While it works about right against Tanks, it is definitely too strong against other targets, giving it no tradeoff. This lack of tradeoff is what makes Tanks seems useless against it.

My solution would be having it affect 45% bonus armor. That way the effect on tanks is bigger than on other champs. The exact value is debatable, but by my calculation 45% should have about the same effect on Tanks in most cases.

What do you think?