I strongly disagree that being ultrawide is an advantage. 16:9 is already wider than optimal for gaming. The human field of view is actually about 4:3. While there is admittedly usually more interesting content to the sides than the vertical edges, I've found 16:10 to be preferable for immersion and would never dream of going wider. If anything, I'd go closer to a square if they still made them.
I'd rather have 2560x1600 than 3440x1440, even though it's less pixels.
IMAX film format has a more immersive aspect ratio too, which is taller still at about 16:11.
I have an ultrawide not necessarily to be able to perceive all my content at once but that I don't need to have dual monitors anymore for putting two documents next to each other without compromising the width of each too much. Even still, I came from a 27" 2560x1440 monitor and the edges are still of value to me in peripheral vision in games. Add in that most 34" ultrawide screens now seem to have a curve to them and it makes visibility at the edges easier as well. Not having to setup an extra monitor and suffer the bezel in the middle is very much worth the troubles for me because otherwise I'd need 3x monitors and at that point it gets insane with multiple monitors in portrait and such.
Try a 4K TV. I bought a card with 4K HDMI2.0 (for 60 fps) out, plugged it into my 46" TV and never looked back. The only drawback is needing to use the remote to turn it on/off. The monitor shuts off with DPMS but when the machine is off it still searches for signal. Doesn't bother me at all
Well, I guess it's down to personal preference, because I would always prefer ultra wide to normal 16:9 for gaming. It's just a much better experience in every way, and going back to 4:3 is just miserable. Again, ymmv.
You're correct that we can only make out fine details in a narrow field of view, but that doesn't mean there isn't value to having more in our peripheral vision. Having extra horizontal width specifically is nice, because of how there is naturally more interesting stuff going on in that range; above and below you is just skybox and ground (for many first/third person 3d games), which you don't really need to see more of.
There is a "regulatory" issue: some competitive games set or used to set a hardwired limit on the vertical FOV, and scale (or scaled) the maximum horizontal FOV to match the aspect ratio of the monitor (or multi-monitor setup).
I'd rather have 2560x1600 than 3440x1440, even though it's less pixels.
IMAX film format has a more immersive aspect ratio too, which is taller still at about 16:11.