It's Time to do Something About Void Staff and Last Whisper!!!!!

Intro I am starting this discussion Because ever since season 5 has started, I have noticed that every one is building either Void Staff or Last Whisper (depending if they are AP or AD). I main tanks, and lately I have noticed that every one is building either of these items, making tanks useless. I understand that there needs to be a balance and a way to counter tanks, but there seems to be an over use and over powered feeling to these 2 items. What I would suggest is just reducing the percentage. By how much? Who can say, but would it be too much to ask for it to be reduced by 5%, its already at 35% (I think that's a little much). This causes the item to be a must have. Just play 3 games of league, I am sure you can observe and detect this pattern of over use.

The Math A character's BASE armor is around 80 and magic resist is around 40 by level 18. This means that fighting someone with out any armor or magic resist, you are having around 28 armor penetration or 14 magic penetration. This is more than most of the flat amount items for armor penetration and about equal for magic penetration items. However, even though the magic penetration item is almost equal, why would you get the flat amount item when its more penetration for tanks, and the same amount for none tanks.