Karthus Ult

So why is Karthus ult allowed to do so much damage? It's not a skill shot, its a guaranteed hit on every enemy, and yet is has such high damage and scaling. Shouldn't the prior 2 parameters mean that it shouldn't be allowed to do so much damage? Typically skill shots do more damage because it takes skill to use and isn't just a single button press or point and click; and if a skill shot does do less damage it would be because it combos with other abilities.

Now granted those are just normal abilities, but shouldn't ultimates follow similar suit? The only other ultimate I can think of that does the same amount of disgusting damage is Malphite ult, and even that falls into the same problem of being scaled way too high. Although I understand why the high ap scaling is there for Malphite because he typically builds tank, so it's to make up for the damage he doesn't build. But even still, Malphite ult is still a skill shot, so if he lands it he's earned the damage and knock up. While Karthus over here doesn't have to risk anything, being able to ult from anywhere (even while he's dead) and get rewarded so much damage for nothing. And the ways to counteract his ult are so limited too: if you're in range you might be able to stun him while he's casting (if he's even in the area, could just be at base); or if you're an ap champ, you would probably have Zhonya's to use.

So off the top of my head there's just those 2 things you can do, not including champ specific abilities that make them invulnerable. I won't include those because it's too specific and those champs wouldn't necessarily always work against a comp that has a Karthus.