I can see why someone might prefer that to reducing the resolution to 1600x900, since it renders a similar number of pixels but the image is still 1:1 mapped.
I don't think I'd want to play letterboxed games though.
I really didn't like it in
The Evil Within for example.
The annoying thing is that you can't have DSR and custom resolutions enabled at the same time.
I use custom DSR resolutions (beyond 4x) so there's no easy way to toggle between the two.
You
can use custom aspect ratios with DSR, but only when downsampling.
So you can't use 1920x800 on a 1080p screen via DSR, you would have to use something like 3440x1440 - which gets you the 21:9 view, but not the performance boost.
It's really stupid that some 'competitive' games have a fixed vertical FoV so that using a wider monitor gives you a larger view.
If they're going to lock the FoV controls for competitive reasons, they should actually lock it so that the view is the same on all monitors.
Pillarbox 21:9 displays and letterbox anything taller than 16:9.
Give those users the option to crop it if they want a screen-filling view, but don't give them a larger view.
Alternatively, give all your players proper FoV controls.
FoV is
supposed to be set based on your screen size and viewing distance.
If you use a larger display, FoV is supposed to be proportionally higher.
This keeps the scale of the objects in the game the same, but expands your view.
Increasing the FoV while keeping display size the same reduces the scale of everything and warps the edges, giving you a fisheye look.
Here's an example I put together a while back, showing how things look if you adjust FoV proportional to screen size.
Scale remains the same on all three displays, the only thing that changes is how much you can see.
The 34" Ultrawide presents a wider view than the 27" 16:9 display, but the 55" 16:9 display presents a larger view than both.
FoV should not be determined by aspect ratio.