I know I've joked about this a lot but honestly I don't really see why the entire league playerbase is so hung up on the concept of melee carries only being the champions that suck. Zed is a fantastic melee carry, he's just also an assassin. I know League players have developed this sort of childlike belief that the only way you can be a carry is to have an infinity edge and phantom dancer in your inventory. Anything less and you're clearly not a carry. However Zed is clearly a melee carry, and so are other melee champions I'll talk about later, and it's why Morello said they wanted to make melee carries more like assassins.
Why is Zed a melee carry?
What happens to zed over the course of the game? He goes from being kinda bad in lane (unless you're squishy, then he can kill you) to end game assassinating tanks. That's a huge jump. Additionally by late game he can overkill ranged carries by several thousand HPs during a burst and can do it consistently and very easily. His abilities also become a lot cheaper, a lot more spammable, and he can start to kill more than one target late game. He also has a 5/10/15/20/25% bonus AD modifier that makes every item he builds stronger and makes his auto attacks massively damaging (400 damage auto attacks +5% current HP ain't nothing to ... mess with.)
Basically over the course of the game Zed just becomes more and more powerful until finally he can just destroy your entire team nearly single handedly. This works really well. In fact, it works so well that it's why Riot is talking about making melee carries more like assassins because all the melee carries (that are good) ARE assassins right now.
Melee carries (that are good) are assassins right now.
Now while you could make an argument that Zac is a melee carry right now that is good he lacks real power end game. While Zac does become stronger and stronger as the game progresses he doesn't do so at a rate that real carries do. Zac is probably the strongest late game tank, but that doesn't make him a carry. Additionally while Shen can carry games early/mid with his split push his split push isn't strong enough like TF's is to really ensure a late game win. It's GOOD, but it's not carry-the-game good.
There are two real ways to carry games: Having ridiculously good split push and having ridiculously good damage. Split pushing often wins games outright by just taking so many turrets that the rest of your team becomes stronger (XP/gold advantage) and by denying turret safety from your opponents (opening up more opportunities for team fights that aren't under turret.) Ridiculously good damage wins games by killing everything in front of you, it's a slightly more direct way to win.
You can also "carry" off being tanky and becoming so tanky you can't die, but given enough time LW/VS will negate this and no more carrying off being tanky. It's true a tank can win a game, but winning is different from carrying. A carry can generally carry the entire team on their own, while a tank still requires that their team be somewhat powerful to kill the enemies while they tank them. A super fed trist can kill the entire team, a superfed Zac can't carry a team if nobody can do damage.
So lets look at currently who is melee and carrying games:
Zed, Kha'zix, and previously Rengar before Riot nerfed him. I'm using Rengar here as a perfect example of a split pusher who carried games. Rengar (used to) become so tanky that it was nearly impossible to stop him from split pushing, while his Q made his damage against turrets far superior to Shen split push. Additionally his ult allows him to easily disappear from a lane and gank another lane even if you try to just 1v1 him to deny the split push. Late game Rengar with his old W heal also used to become practically unstoppable in team fights as he just healed so so much. His amazing split push, his amazing late game tankability, his ease of turret taking made Rengar one of the deadliest champions in the game and let him carry easily.
Although this only happened at the high ranks and in touranments I think enough still watched this happen through the streams to understand exactly how Rengar carried games through his split push.
Kha'zix and Zed though are a lot more direct. Zed can kill anyone that is currently living with his ultimate, and his auto attacks + abilities do enough damage to continue to kill opponents. If you can do an assured kill and still exist that means Zed turns every team fight in to a 5v4. Unlike other assassins he lacks neither the sustained damage nor burst damage to always ensure a kill and still be useful afterwards. Diana by end game sometimes lacks the damage to kill an ADC through barrier + bulwark + other various shields. Zed can straight kill an opposing ADC with his ult, then still have his spammy E and auto attacks doing insanity damage (+25% AD) to continue to kill other people.
Kha'zix has resets on his leap and a very low CD Q. Yeah. His is much less exciting than Zed's to explain because everyone understands it and it's not exactly hidden. I'm sure we've all lost to a fed Kha'zix carrying multiple times this week alone.
So Riot wants to make melee carries more like assassins.
Morello said that, and I won't quote it because I don't feel much like finding it. But if you want go find it. Melee carries can't just be ranged carries except they melee. That won't ever work. Nobody is gonna play an AD Yi competitively because it's just far too easy to shut him down. Everyone is going to play a Zed competitively because he just works. Same with Kha'zix. So Riot looks at those two champions and says "well this is working... this is working really well... we should just make out other melee carries like these guys." And tada. I'd go on but I think I covered it really well. Master Yi doesn't work, melee carries can't be auto attack focused. Kha'zix DOES work, melee carries need to be ability focused.
AND YES, that's what this comes down to. Ability focused melee carries with some survivability WORK. They can carry games, they are melee, and ... well that's all that's required for a melee carry. AUTO ATTACK focused melee carries with no survivability do not work. Additionally having some ranged poke works wonders for the viability of melee carries. So that's really what it comes down to, and why we'll see a lot more of champions like Zed and Kha'zix, and older champions getting revamps to look more like them. Expect this, it's whats coming.
It's why Fiora is both ability focused and auto attack focused, which could work mind you, but more to the point it's when Riot started to experiment with more ability focused/assassin-y melee carries.
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