You said you don't like the thought of 100-0 somebody
I think it's more "Riot doesn't want a champion to always 100%-->0% things" over "they don't want a champion to 100%-->0% someone".
If you look at the QWER rotations of assassins, there bases only tend to allow them to take out ~50% of their own base HP at any given level. It's around ~40 base QWER damage per level vs. ~80 HP per level, for ~1000 QWER damage @18 and ~2000 HP.
You also need ~450 AP to double the QWER burst of pretty much every AP, as AP scaling usually stays to a consistent ratio compared to the base values.
Anyways - with pretty much every QWER bursty champion, you have to exploit 1 of 3 things to actually 100%-->0% someone:
- Be a higher level, giving you more bases and your opponents less HP. Basic reason to send a mage or assassin mid right here.
- Have more items/gold. If you have an item advantage, you can usually get off the extra DPS needed.
- Target someone who's completely ignored defense.
So - yeah, they don't allow any champion to 100%--0% someone just as a shtick. It's an option you can aim for, but your opponents always have a way around it.
The main thing Riot doesn't want is just 100%-->0%ing someone with no way of preventing that from happening (outside of never going near that guy ever).
Veigar is (was) kind of problematic in this regard for 2 reasons:
- His infinite AP scaling potential let him get to a point in a realistic game-length where defensive items didn't really slow him down at all.
- His stun-ring allowed him to 100%-->0% a target from fog of war with 0 warning. At higher Elo's, Veigar can reliably land the edge of the ring on targets 1075 range away from him, stunning them for 1.5~2.5 seconds: certainly long enough to fire off his QR combo.
Pretty much every mage actually requires a skillshot that's telegraphed and fairly slow-traveling to start their QWER rotation, and most assassins don't have any CC at all (which usually opens the possibility to use all your abilities, summoners, and item actives to deal with that melee champion that ran at you).
And when you do come into point-click CC zones: having ~600 range is generally a major limitation of point-click stuff, you pretty much never get 1000+ range with point-click, making Event Horizon extremely powerful.
While Riot's reasoning is kind of derp at first glance and doesn't go into this much,
Veigar's identity is very much tied to his QR burst and infinite-scaling,
not so much Event Horizon.
As both are a potential problem in the 100-0 someone with no (basic) counters working against that, along with Event Horizon quite possibly being the single strongest QWE CC skill in the game and one of the best QWE skills in the game in general, it's a clear target for any nerfs to Veigar for any potential problem he brings.
All that said - it's kind of sad to see a champion like Veigar nerffed, but it's really important to keep in mind being OP and lacking counter-play are 2 very different things.
Zed is up at the top because all his skills are extremely telegraphed, you can dodge pretty much his entire combo, his ult gives a clear warning to activate Zhonya's / QSS / Exhaust, and he's actually playable despite those weaknesses.
Talon on the other hand got a brutal nerf a few months ago because he could leap directly behind a target from 700 range instantly with no warning or chance to catch him in traps or skillshots at all, silence his target (disabling all their abilities, summoners, and item actives) and then dissapearing into a flurry of blades rending him immune to all point-click mechanics (auto-attacks).
Outside of a few months after his release when AD caster itemization was awful, Zed's pretty much always been a solid pick and Talon hasn't because Riot felt the difference in reaction time and counter-measures between the 2 is a very significant advantage in Talon's favor worth it's weight in more tangible stats, which has unfortunately made Talon an unreliable pick because he's balanced more in an "he might obliterate them or might fall short" zone of balance, where Zed's abilities place a greater emphasis on skill over chance, making him more reliable (and thus better) in pro play.
Veigar has the Talon problem, so he got nerffed rather swiftly when he started seeing competitive play.