Talk:Katarina/@comment-137.226.66.4-20120326074428/@comment-116.237.40.240-20120326114811

I honestly don't know, but I'd have to say it's because AP items give more utility. There aren't AD/Armor items as good as Zhonya's (Zhonya's scales better than Atma's on Kat), and you'd probably end up building a bit of AP in the Gunblade for the spellvamp anyways. It's worth a try I guess, but 3 BTs give 300 AD at max stacks, with another +40 AD and +70 AP from the Gunblade and +70 AP from Void Staff (because you still need that mpen), whereas Rabadons + Zhonya's + Gunblade + Rylai's+ Void Staff gives 689 AP and +40 AD from the Gunblade. This makes the BTs do 2476 damage from the Q, E, and the ult, whereas the AP build does 2712.4 damage from the Q, E, and ult. However, if you were to autoattack once after E using the AD build, you'd do 2816 damage. The problem with this is that Katarina would generally be MUCH, MUCH squishier using the AD build, whereas you're still somewhat tanky with the AP build. If you argue that the numbers in the AD build have been lowered due to the Void Staff in the AD build, the problem is that all of Katarina's skills do MAGIC damage, so if you don't build any mpen, you'll do no damage.

tl;dr: The AP and AD builds do comparable damage, but the AP build makes you tankier and gives more utility such as a slow on your spells and invulnerability from Zhonya's. The AP build also has significantly more health and resistances.