I did explain situation in other threads. In PvP you do not have “Side Scroller” mode, Each view of opposing team is rotated by 90 degrees.
This means that you can be shot offscreen by other 16:9 users if you stand in wrong position. And that 16:9 user can offscreen users that have 21:9 and stand in wrong position.
Generally, wrong positions are when you go down and in right direction if you start at left side from your point of view. Or going down and into left direction when you start on right side from your point of view.
In other words, 21:9 only exaggerates effect of good vs wrong positioning. And this 90 degree rotation is actually balancing fix for existence of any non-square screen. (Yes, all screens are non-square and only balanced screen is square screen. Nobody has that. Want it fair, then suggestion would be Fog of War in circular shape. And 16:9 will have to sacrifice 7 out of 16 width units.)
Are you asking why only circular vision would be fair when “nerfing” takes place? Well, there are 16:10 screens which have less wider view than 16:9. And if 16:9 are eligible to demand nerfing of 21:9 screens then 16:10 are eligible to demand nerf of 16:9 screens.
Then someone with 4:3 screen ratio (1600x1200) comes and demand nerf of 16:10 screens because there is precedence for nerfing.
And right after someone with old 5:4 screen (1280x1024) does same to 4:3 screeners.
See, nonsensical. Secondly we in west may think that 16:9 are common screens. Well sorry. Game revolves around Korea. Our display market is 4~5 years behind theirs. 21:9 is common resolution there.
Now drop of reality.
Someone has quite affordable 35’’ 21:9 screen with 3440x1440. Has good FoV.
Next to him is guy with 50’’ 16:9 - 4K screen (same price) which enables 21:9 mode. His effective game area is actually 46’’ in diameter, and his resolution is 3840x1648. (Yes, in any sense better than regular 35’’ 21:9 screen, except he sees black bars above and below.)
So when someone with 24~38’’ 16:9 screen complains about existence of 21:9 mode, they complain about their choice not to buy larger 16:9 screen or not buying Cinematic format 21:9 screen.
Now, to not be so triggering on every step. 21:9 screens have disadvantages too. Not in LA, but in any game that has locked horizontal FoV instead of Vertical. Like Counter Strike. If you have 5:4 screen you can see same angle to sides as 21:9, but 21:9 is almost blind in vertical angle in comparison.
Nothing is for free, would you enforce black bars on 16:9 gamers in CS just of acommodate fair play for 21:9? I would not. People chose screens it has consequences. Fact that SMG added virtual 21:9 for other aspect ratios is actually showing that they cared and did think about problem.
Their solution of 90° rotation of viewports is good and smart. People that complain did not know about it, or did not comprehend how this game mechanic works. (I expect OP simply did not know.)