Hey! Unfortunately, "frustrating" is the main reason why we nerf legends. Win rates and pick rates are good proxies for how dominating characters are in the game, but the goal of nerfs and buffs isn't to move win rates closer to 50% for some abstract philosophical reason. The ultimate goal of buffs and nerfs is to make the game more fun for everyone. In this case, as Spock would put it, the needs of the many outweigh the needs of the few.
Before we go too deep down this rabbit hole, let's talk about what the nerf does and doesn't do. The nerf makes it so that things that were previously blurry are no longer blurry while in the gas. That is literally it. You still can't see through the gas, vision blocking gas still lingers on your screen after you leave the gas, you're still slowed and unable to sprint while in the gas, and you take MORE damage now than you did before. The time to kill a full health legend went from 13 seconds to 10 seconds. Also further increasing damage and slow is absolutely on the table if necessary. So saying that "they can now run through the gas with almost no damage" is a bit of an overstatement: they are still just as slow as they were before, Caustic still sees their highlight, and they take MORE damage from the gas now than they did before.
But it IS a nerf, make no mistake. We don't know how big yet (it takes a few days to get good data), but I wouldn't be surprised if this ends up being 1%-2% nerf, which is a very bitter pill to swallow on a Legend that was already at 47% trios win rate before this nerf. Caustic is the number one legend on my list for a buff; but I've got to find a good buff that doesn't reintroduce the level of frustration that trying to fight inside the gas was.
So let's talk about power vs frustration. Some game mechanics are extremely powerful. Some are very frustrating to fight. (As a game designer, I use the technical meaning of frustrating: you're attempting to achieve a thing but the game won't let you; that thing could be offensive or defensive in nature) (also as an additional note, frustration is the core of PvP design; frustration is the friction you must overcome to win; with no friction, wins are meaningless and arbitrary) Not all powerful mechanics are frustrating, and not all frustrating mechanics are powerful. This makes game balance so hard to do. Take for instance Octane's passive heal. It's a very powerful mechanic, and yet I buffed it this patch. Why did I feel I had the leeway to do so? Well on the one hand Octane has a high encounter win rate with a low trios winrate combined with a high pick rate. My analysis is he's a super fun run in and kill/eventually die character, creating a lot of Good Chaos. I saw his pickrate fall off toward higher skill and figured that while this change wouldn't turn that trend line around, it would extend the skill range to which he's picked. That's the data side. But more importantly? Experientially, Octane's passive heal is not a FRUSTRATING mechanic at all. It's almost pure upside. Octane gets to feel super good about it and feel unlocked about using his tactical, while to the enemy the mechanic is entirely invisible and doesn't enter into the equation in the middle of a fight. This is the dream.
Fighting in gas on the other hand may not be a mechanic that is particularly powerful for Caustic (if the player in the gas is close enough to the edge and better at using guns, they will still tend to win) but it is incredibly frustrating for the other player. You know Caustic has an information advantage (he sees you better, you see him worse), you're slowed and so dodging is out of the question, and you slowly take damage, which ramps up if you don't leave the gas, putting you in Zugzwang (a term from chess which means you are forced to act and your enemy can capitalize on your action). All of these things are immediate and feel incredibly stressful (you have to move NOW! And the cards are stacked AGAINST YOU!), even if as I said before, if you have better gun skill and if you're playing a character with a smaller hitbox than Caustic, you're likely to win anyway. That's what I mean by not every frustrating mechanic is powerful.
So all the things I mentioned above are STILL TRUE today after the nerf. If anything, they're more true with damage starting higher and ramping higher; you have a whole 3s less to get out of the gas before it straight up murders you, and every second you do spend in it makes you a lot more vulnerable. The only thing that's changed is that previously in order to express your better gun skill, you had to overcome blurry outlines and a blurred sight. This made it incredibly hard to know what you were aiming at and was just downright unpleasant. It almost would have been better to say "you just can't shoot", because from my experience even if you did turn it around and kill Caustic, it was an awful experience. Seeing everything blurred just feels bad and there isn't a way to get better at it.
All this to say: we hear you and it feels unfair, especially if you assume that all our balancing decisions are made based on data. It makes sense that you would think that: I personally bring up our data a LOT when I talk about why I buff or nerf characters. But in the end data is just one of many signals that goes into the buff/nerf decision, and the only reason we care about this data is because we believe it describes underlying trends that can end up making the game less fun in the long run. The goal of balance is a fun game, not win rates at 50%.