Karthus's Q has no indicator when casting: Reasons why, and why it should.
Let's talk about why it doesn't currently. Namely, it has an extremely short cooldown for a ranged ability. And the other reason being, I think, that it's simply left over from problems with his original animations-- his VU being one of only four that had no ability changes whatsoever (the others being Heimerdinger, Twitch and Annie). The old animation was extremely misleading for the enemy, having the same AoE that it currently does, but with a warning animation less than a quarter of the explosion radius, as you can see here:
https://i.imgur.com/EqeImTi.png
(I tried my best to size things correctly) But as you can see, the new animation actually shows the circumference from the start of the cast all the way until the animation is finished. With nothing but the tiny orange skittle at the start of the cast, the original animation was incredibly unfair, but was made more fair by the caster being just as uninformed about the radius as the enemy.
The new animation actually solved all the issues that made the forced-quickcast necessary in the first place:
- Since it's no longer misleading to the enemy, the caster doesn't need to be uninformed to compensate.
- And while it does have a short cooldown, that was only unfair when the enemy was mislead by the visual. Now that they are shown the radius as soon as the cast animation starts, rather than only when it pops, they can sidestep or dodge it reliably.
Conclusion: The forced quickcast-without-indicator for Karthus's Q is outdated, as its new (2014) animation fixed all the issues that made it necessary in the first place. Effectively, the enemy now has more of an indicator than you do as Karthus-- since they get the whole cast time to react to the ability, while you don't get the indicator before casting to see whether or not you're actually only hitting one enemy if they're grouped, or if you're even casting it in range.
Solution: Take away the forced quickcast, and give the ability the indicator it's supposed to have. If someone wants it the old way, that'd still be an option in controls.
I'd also like to note that it is a major outlier as far as quickast abilities are concerned. It is one of only two forced-quickcast ranged abilities, the other being Yasuo's tornado. And it is the only forced-quickcast ability in the game with a delay. The rest are instant-cast self-target AoE abilities, which makes sense since they're generally on melee champions who will be in range of their target anyway.
And this is one case where the opinions of people who main the champion would actually be a detriment to the discussion, as they have the most practice overcoming this unnecessary disadvantage and may say it has less of an effect than it truly does.