The reason why the new AP items seem weaker...
Is because Riot is clearly playing it safe, at least in my opinion.
The marksmen patch wasn't the most well done patch, to say the least. It got a ton of hate from every man, woman and child. Why? Because the weapons were overtuned, overpowered. Of course, Riot would go on to adjust and nerf accordingly and the community eventually grew accustomed to seeing Graves , but I'm sure it still left a sour taste in Riot's metaphorical mouth.
And right now, Riot is doing the exact opposite. All the items are now underpowered, and this is probably on purpose. It's the same thing you guys, but reversed. They'll eventually buff the items accordingly, but they're trying to keep everyone satisfied.
Then again, I may just be wrong.