Karthus Needs Some Buffs

Support mages, melee carries, assassins. They all have two things in common: The capability of being a mid-laner, and the capability of countering .

Now, I know that Karthus isn't countered by everyone, but if you have played the game enough, most to all champions played in mid lane are the three types listed above, and it would seem as if there are more champions that counter Karthus that don't counter him or by countered by him. In general, high-DPS and/or tanky champs can take the Deathsinger and squish him into the ground. This is why I think Karthus should get some sort of buff; this would also help him shine as the late-game mage that he really is:

Q: Scaling should be the same, but at max rank it would be nice if he could do more damage the longer he attacks an enemy with his Q; it doesn't have to be that much more, but it can stack several times and do around 20% extra damage or something like that at max stacks (the number can easily be changed).

W: The slow and decreased MR is definitely good, but at max rank it would be great if it would apply damage reduction of some sort, possibly scaling from AP. Not too much reduction but it would apply to anything the victim would attack.

E: Perfectly fine; can stay the same.

R: Does more damage at early ranks and early game in general, and also does extra damage at max rank based on how much health the target is missing.

TL;DR: More damage with Q the more times you use it on the same guy, damage reduction with W, and extra dmg based on missing health for R, all at max rank.

You guys could probably argue how he doesn't need a buff or this buff is too OP, but I would appreciate constructive criticism and/or what you think a buff for would look like.