Sorry, I need this explained to me a bit more.
It's OK for Randuins Omen, an item designed to counter Critical Strikes, to counter Anivia and Karthus. Champions who don't have anything in their ability description saying that they crit, many of their players don't know it's a crit, and who aren't able to benefit from crit amplification... But they can be hurt by crit reduction?
Now we look at Jhin, who the player knows that Attack Speed translates to Attack Damage. A Jhin player, hit by an attack speed slow, would expect the damage decrease, regardless of if the person causing the attack speed slow expects it. And for some reason not all Attack Speed modifiers count against him?
Sorry, the reasoning is completely backwards. Why is it when the player expects to be adversely affected by something it's prevented, but when they don't expect to be adversely effected it's allowed?