Zed doesn't need nerfs; Bruisers need Buffs
Before we go off the rocker and whine about Zed just because he's FoTM, let's take a moment and and objectively realize his kit is not 'too strong to be balanced', it's a simple issue of Assassin's being remarkably powerful in this current meta because the Bruiser class that once acted as a bridge between Carries and Assassins has been nerfed to hell and back, now there's nothing to offer a check of balance or structure between Carries and Assassins. Carries kill everything fast, Assassins kill Carries even faster.
- Damage is King S5. AP Mages, ADCs, and DPS champions in general are stronger than they ever have been before in league history.
- Players are rewarded heavily for stacking damage, while defensive items have been nerfed repeatedly and are generally inefficient.
- Dragon and Baron no longer give any defensive value, penetration items are straight up overpowered, Dragon stacks scale outrageously hard with offense, offensive masteries are stronger, offensive items are stronger, and all the while defensive items have only gotten weaker.
Now, with all these glass cannon champions running around, it's only natural that champions who can reliably gib glass cannon champs are at the peak of their strength - aka assassins.
http://www.nerfplz.com/2014/12/2014-champion-tier-list-solo-queue.html If we look at Tier lists, we'll notice it's not Zed who's Top tier despite the frequent complaining on GD, but rather Katarina, Akali, Fizz, Talon, Ahri, Syndra, Annie etc. who dominate the Assassin scene. Zed is not God tier, not tier-1, but down in Tier 2 with the likes of Mordekaiser and Diana.
Why is Zed rated so low? Simple : because his burst is slower than a lot of assassins, he's more farm dependent on most champions, and his base stats alone are unlikely to gib anyone unlike other champions who are rated above him. So despite his relative safety, he's not gamebreakingly strong - maybe he's just annoying because you aren't killing him a whole lot while he may be killing you in lane several times, so he feels stronger to you subjectively
Now back to the underlying issue: Bruisers have been hit too hard that they can no longer fill their roles as front line fighters or as anti-carries.
This is due to a great series of reasons, some of which include defensive item nerfs, carry item buffs, mobility creep, utility buffs, dragon/baron changes, and meta shifts. There's the blatant issue that it's almost never worth it to build off-tank (aka traditional bruiser) because:
- Even with 2 or 3 defensive items, you're probably going to get melted in a few seconds anyway. Defensive item's really don't do squat, it's much better to rely on abilities such as Troll-pole/dodge/Zhonyas/Troll-pool/etc to stay alive, or synergize with extreme defensive steroids like Alistar Ult. For most champions, defensive items are borderline worthless.
- If you don't kill the carries nearly instantly, you're going to get peeled. Unsurprisingly, this is another contributing factor to why Zed is so low tier despite his strengths - he just doesn't kill fast enough. Utility has been heavily buffed, it's a simple matter for almost any viable Support to CC-lock a Bruiser long enough for carries to wipe him off the face of the map.
- If you rush defense, you will lose lane. All defense items do is make you die slower, they will not win you trades.
- The less offense you have, the less Dragon will benefit you
It doesn't take a rocket scientist to realize to fulfill the role of anti-carry in this meta, you need to be able to easily and consistently insta-gib. The game's come to the point where innate abilities in junction with item actives like Zhonyas grant better and more consistent survivability than straight defense. Everyone is squishy in their vulnerable moments (Zhonyas on CD, Getaway on CD, peel on CD, caught out alone, Troll-pole on CD, etc) and it's Assassins who have high mobility, fast gapclosers, and strong upfront burst who capitalize best in this current meta.
TL;DR Zed doesn't need nerfs, the meta needs adjustment. It was Bruisers who kept Carries and Assassins in check, and with Bruisers nearly forced completely out of the picture, the meta has devolved into unsatisfying Assassins vs Carries