My issue with AP itemization is the early game stuff
I don't really feel like the late game options are as lacking as people claim. I think there is some merit to the pushback against the mage circlejerk mostly because mage items come with a lot of utility that people don't seem to appreciate enough.
My problem as a mage player is the lack of options during build paths to my items and also starting items.
We start
because we need the mana sustain. While it does let us start with 2 potions I don't think that makes up for the lack of flexibility compared to ADs who can start
,
, or
depending on the situation.
Now here are some early items in AP build paths
,
,
No health sustain or defense. I feel cold, naked, and vulnerable.
Have to earn stacks to get a lot of the armor, no health sustain to make it help vs AD poke, and doesn't do jack shit against things like Zed's all-in. This is a dead slot until completing 
,
These are actually really good and have a noticeable impact on early-midgame. But there are gaps that they do not cover, like sustain and mitigation. Also,
is too niche because very few mages can benefit from rushing Liandry's so it would be nice if it built into 1-2 other items. As is it is now, it delays your build too much on most mages.
Now let's see what AD champions can get.
Anti-burst, also the MR actually goes a long way when you have lifesteal...
...Which brings us to this
Health sustain means that any damage mitigation is actually useful. This also builds into a million different things.
Oh look, their MS item has health too.
I find that there's a power dip as I'm sitting on weak items and that is what isn't working for me as a mage player. The completed items are mostly not as bad as many people claim, but having to farm them while AD champions enjoy better build paths to their items is tough.