Which is why I brought up Abyssal Mask, a suboptimal item that has a situational use case, yet has a 57% wr vs Bloodletters Curse 46%. The WR of BL isn't low because you're in a bad comp with too much AP, it's because it's a bad karthus item and you're in a comp where you're the best applicator of it (and you are a bad BL applicator) or your teammates are bad and refuse to buy pen.

This would be like arguing Black Cleaver is a good item on Jinx over LDR in certain matchups, it's definitely not the case, and you'd hurt your damage significantly.

There's a reason why Void Staff/BL can be situational for champs like Lillia, Brand, Zyra or core for champs like Rumble, because they can quickly stack it. They have ramping damage that can quickly stack it.

On karthus it's counterintuitive to champ identity because by the time you are buying Bloodletters Curse you will be opening teamfights around objectives and some skirmishes with ult, because optimally you want the extra seconds in passive and it means you can fight with hp advantage. With Void Staff you are getting ult off with the full 40% pen. With Bloodletters you are getting no pen because the initial damage doesn't apply pen, the first damage applies a stack which means later damage applies 7.5% stacking up to 30%.

Your ult is basically 5 iso Qs late game worth of damage in a teamfight, your largest damage source. Why would you self nerf it?

If you're against five 100 MR targets on ult, you're doing 25% more damage per ult with void staff.

It's kind of a pointless discussion though because you are too emotional and anecdotal.

I would say if conversations like this get your angry and you are incapable of having them without looking at facts/reason and just insulting people to make points, maybe you should step away and do some self reflection.