I'll take a crack at this. This gets long and I pull information from experience. I'm a new poster and not a forums guy so, I apologize if I offend anyone with my ignorance of forum etiquette/norm. I'm just looking to give information/perspective.
Note/Disclaimer: I am biased. I'm an Ezreal player and he's one of my favorite champs. I definitely don't want a nerf. I do not have as much experience as perhaps a top-tier player, but I think I fit the bill as good Ezreal player. I recently started playing ranked games and went 4-0 with Ezreal where-as I am 1-1 with Galio and 0-1 with Garen.
Now, to address the phrase OP. I'd argue it's a hero that, with minimum skill/effort, can dominate a game entirely at most tier levels. If not the first case, I'd argue it's a hero that can, at top-tier play, always win a game on its own or, by mere presence, shift the entire tempo/response of an enemy team.
First, Ezreal is not a minimum skill/effort hero. He is if you want to deal damage and be a threat. But to reach unstoppable, he is not. You need to hit nearly every skill shot, know when to hold and use the ultimate, have a strong build (I have only seen unstoppable AD Ezreals) and a great understanding of how team battles function.
Second, in top-tier games he cannot win a game on his own. Too many good players know how Ezreal works. All they have to do is sit back, farm a bit, and hope the other lanes are out-producing during early stages. Ezreal has very little denial abilities. He deals a lot of damage, but you can both out-farm and out-push him in the early stages of the game. I’ve played a lot of decent Ezreals where they CANNOT get a kill off me. Wards prevents ganks and staying back prevents confrontation.
Lastly, an Ezreal in the thick of things is NOT unstoppable. Any Ezreal who uses Arcane Shift to initiate or deal extra damage in an ensuing team fight is asking for (of good players) to focus him down instantly. He has zero survivability. What he has is mobility and here is what makes every person say he’s OP.
Mobility is incredibly important for a ranged carry. Think about Ashe and Twitch, both can deal damage, both can initite/escape/slow. But what do they lack? They cannot flash indefinitely. They cannot stun indefinitely. They cannot slow indefinitely. Can Ezreal? No. But let’s say you hold Flash with Ezreal. At worst case scenario, you can shift out of a gank, flash out when they focus you in the team battle (if shift is on CD), shift again by the time you need it. If you’re holding ghost (I often go Ghost and Flash), you can ghost to run or chase, and then shift again. That is 5 movement-spell casts in 20-30 seconds that gives him CONTINUOUS mobility.
Sure, Ashe can slow/stun, but those skills can be responded to with Cleanse and Merc. Boots. You can’t respond to flash/shift/ghost. Sure Ashe can pack ghost and flash, but she cannot re-engage. Once both are on CD, Ashe is done as far as escape/mobility goes. I don’t know how many countless battles I come back in with Ezreal at 50 health just to deal an extra 1-2k damage and still get away (more often I make champs chase me and take more damage or force a champ to back off an ally).
So, after establishing that Ezreal has immense movement potential, let’s see how it works in his favor.
One-on-one he literally has no risk. He fights you, if he’s winning, you’re dead (he can chase you). If he’s losing, he gets away; his spells are on cooldown. Great!
In ganks, it’s even worse. I’ve rarely gotten into a situation where 2 heroes gank me and I am so totally baffled/screwed. I have shift, ghost, and flash. Come on… so you send 5 members to gank me. How many times are you going to do that? Seriously? The rest of my team is farming and pushing, you can’t respond to 1 hero with ganks with the risk failing being so high. I’d argue Ezreal has one of the highest escape rates even if all 5 enemies DEVISE and EXECUTE a plan to get him.
Now, in a team fight, you have a big problem. Ezreal will likely be in the back lines. Now, the problem with focusing Ezreal is that he can true blink. This means you need at least 2 heroes to chase it just to tank through the enemy damage. Let's say you ignore it, it's hammering 500 damage shots in your face. Ashe can’t do that. Ashe needs to ulti you and get within auto-attack range. Ezreal does not. He can sit back for hours and still produce damage with the OPTION to get closer or go farther. What Ezreal does is put you between a rock and a hard place. There is no "do this and it's stopped." You take gambles. In any game, the more gambles you take the more uncertain your outcome.
If one hero is making you take gambles, if he is on your mind, then that is already a distraction. This is what makes Ezreal OP. He has a lot of options. He can respond and adapt to the team fights. He is strong in the beginning in that you either don’t kill him and stalemate a lane or he kills you. That’s not a fair trade. Two heroes should have a = chance to kill one another or one does something better than the other to compensate. Late game, he is an un-focusable ranged threat.
So, how do you nerf that? You can lower his damage, but then he is unplayable at lower tier levels. I’ve seen too many people use shift to actually CLOSE the gap between an enemy team and themselves. These players rely on the fact that he can deal burst damage from a distance.
What you would need to do is make Arcane Shift have a higher cooldown, make it less ranged, and maybe even make it not passable through walls. The way to nerf Ezreal is to take away his options. You can’t do this without changing the champ IMO. So, in my mind, it has one of the highest potentials out of all the heroes, but the tradeoff is immense skill. You need to be a very skilled player to make Ezreal unstoppable. This refers to probably 5%-10% of the population. Because skill cannot be learned. You can’t just take a build order and make him rigged. This is what made Heimer, Shen, and Jax (pre-nerf) so rigged. With minimum knowledge and a pre-made build, they can become OP pretty fast. Ezreal is not like that.
I hope this works to clarify Ezreal as a champion. I don’t know if a nerf is necessary, but I believe this answers the original poster’s question.
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