Why should Viktor's core have the highest AP come late game AND a ton of mana?

I didn't get stomped by a Viktor, but I did play against one.

It occurred to me that his Hex Core is the 2nd(with passives)/1st (without passives) strongest scaling AP item, why is his Hex Core able to have the highest end-game AP (besides maybe Raba) as well as offering more mana than even Morello? All for a total of 3k gold. ALL while he gets upgrades to his spells along the way. He gets a 3k gold Raba in terms of AP amount (not the passive) at level 13 or so along with...about 300 mana or so.

This item allows him to clear a wave more often than anyone that doesn't build a mana AP item, and doesn't even have to be there since his lazer echoes its damage. With just Raba and the Perfect Hex Core, he has 405 AP at max level. But since he usually fits a Rylai in his build, it'll probably be higher.

I'm not asking for a nerf to its damage, but it should not have as much mana as it does...if any. Gotta limit him somehow, no? Limited behind a 3k gold wall that upgrades its damage and mana, as well as a spell along the way...In 1k increments. With the waveclear he gets after the initial 1k (which, is not hard to get in the first 15mins or so), it pays for itself.

I'm sure downvotes will happen, but it doesn't make sense that an item that is central to his kit (and permanently) is also the strongest AP item outside of Raba or Seraph's.

Maybe if it had less to it, he wouldn't keep getting changed or nerfed.