Originally Posted by The Sherminator
On the contrary, a gunblade which yields AD and AP while giving you a slow to force someone to linger in your ulti longer than they would like is a hybrid item that synchronizes fairly well with her kit.
Some stats to begin with yeah?
Stats +45 attack damage
+65 ability power
+10% life steal
+20% spell vamp
Passive Unique - Reload: Your basic attacks and single target spells against champions reduce the cooldown of this item by 3 seconds.
Active Unique: Deals 150 + 40% of your ability power as magic damage and slows the target champion's movement speed by 40% for 2 seconds. 60 second cooldown.
Rylai's Crystal Sceptre (2900g)
Stats +80 ability power
Passive Unique: Your spell damage will slow the target by 35% for 1.5 seconds (15% for multi-target spells, damage-over-time spells and spells with a cooldown time below 3 seconds).
So rylai's slow is on every spell cast and therefore for the duration of her ultimate. Gunblade's is 2 seconds.
Lifesteal is essentially wasted so you're paying for stats you won't use (or at least won't use much of). Gunblade's active as damage is meh unless you have good AP. It's also around 500 gold more expensive and gives less AP. Build path is better on Gunblade though, with shorter gaps between potential purchases.
Gunblade does give spell vamp though; remove that spell vamp and see how many Katarina players still build Gunblade. Yeah, it's not the slow, but, you're right in that the slow is useful (i suppose). Also Katarina players do like that Gunblade. I just feel it's not as good as it could be for Katarina.
I think Katarina's AP ratios are around 3 AP. That's reasonably decent for a AP (although with the removal of AD ratios hopefully she's gain more AP ratios). She also scales with AP on every ability. She's better as AP. AD Katarina needs to go away already.
She's be easier to balance, better to play as, easier (more effective) choice of items, and you wouldn't be purchasing items that give stats you don't need if katarina was a straight AP champion.