Why is AP Lucian so weak compared to AP Ezreal/AP Kog/AP Varus/ AP Corki/ AP MF?

All of these champs have alternate play styles which I do applaud riot for making it happen because it gives the champs depths and customization that can be explored by the player.

But when you look at AP Lucian, he is really weak when compared to the rest. He only has 2 AP abilities one of which being his ult. When his ult is on cooldown, it leaves him with one AP ability.

To top it off, going AP means i'm giving up heavy crit damage and the benefits are not worth it.

For example, Lucian ult does practically the same damage whether he build crit or AP, and it still takes like 3 seconds to kill a squishy late game. Late game is the point at which a master yi can kill you in 0.5 seconds.

Overall, AP Lucian W/ult, is not worth what he is giving up for not building crit.

I'm making this post in hopes that riot would just shed some light into what they think of the stat of AP Lucian.