We need more variety of AP items
Nowdays its all about
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If youre a DoT throw in
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If it works use
If youre melee or use
If youre akali use
If youre vlad use 
Most AP items right now are very situational and 80% of the time the top one is used
Besides
ADCs get to chose
Thier lifesteal item
Their as/crit item
Their pen item
Free 30% cdr with crit mana and damage
Choices of tanky item

The only adc item that is less versatile is
for champions like
and even then it give the opportunity for bruisers to get.
Pls give us more choices for ap items