Which is an illusion as you could draw a 4:3 box around the gif and then shrink the image and put black bars above and below for the widescreen ratios.

The merging of computer monitors and consumer TVs sucked. A shit refresh rate and crap screen ratio was worse for gaming.

No, it's not illusion for the most games. For example, I played Diablo III on 4:3 monitor but this game has special mode to have these black bars above and below, but for the other games such scaling presented in this gif is very true and used by default.

Another example of CS:GO - https://www.youtube.com/watch?v=qCCwgUrBpI0 - you see more on both sides in 16:9 mode - vertically it's the same.

It is an illusion as you could shrink or enlarge the image with mods and in a game like that you would want to see above and below as much as from either side.

That's only possible IF there are mods for the game - most of the games have NO mods.
Also: not every game publisher accept such game modifications (for example: Blizzard is very strict on what is / isn't allowed).

16:9 format monitors allow all this without any 3rd party mods and are more universal for everyday use.

The thing is:16:10 does not give you vertical advantage in most games - in most games you vertically see the same as in 16:9.

Uhhh... I don't think you have it set up right. None of that should be happening.

Oh no, black bars. Why do folks get their knickers in a twist about having a game in its native resolution? Next time, I recommend researching a monitor that suits your needs before folding to a trend.

May I ask why you consider better than the standard 1080p?

Much better for work and some games. No matter what aspect ratio you have, it is bad for some games. I see no problem with having slim black bars in some games and rather that than three differnt monitors, one for each aspect ratio. Sure the wide formats are just perfect for some games and film but those would show just fine on a higher screen too if I set up the screen's settings correctly. Another solution would naturally be to have a much bigger screen, many of which take more space, where there are enough pixels vertically anyway. Problem there is cost; more expensive monitor + more space (a bigger flat might set you back A LOT) and a much more expensive graphics card to push so much more pixels.

For me 16:10 is only better if you are using monitor mostly for work and you need space but you can't afford anything better than "standard" 16:9 (like 2560 x 1440).

In any other situation 16:9 is better as it is currently more versatile format.

I was talking about a 3660 (or whatever) X 1440. 30 something something.. .real wide. I tried every resolution available on Fallout 4 and ALL resulted in large parts of the screen not being used. Again, I _could_ scale it take up the whole page, but then it just looks awful (stretched).

I think maybe these monitors are more for productivity than gaming. So it was my bad for buying it.

Just some whacky out-of-the-box thinking: Have your tried researching the actual native resolution of your monitor (which usually doesn't include "or whatever" in parantheses) and then setting/modding the games to the correct resolution?

Yes, that's true. 16:9 is the current standard one, 16:10 is sometimes natively supported, sometimes not. And if not, then people will probably have a little different experience (most probably worse one).

I don't know if you're being a smartass or are genuinely confused but I'll give you the benefit of the doubt. The native resolution is what I said above, I was typing from memory but it is a well known, ultra wide resolution. As I just looked it up it's 3440X1440. And as I said above I tried every resolution in Fallout 4 and got the result I posted above.
These are much better suited to productivity than gaming. At least at the moment. And I wish I hadn't bought it but live and learn.
It's set up right.

Donm't give up on it. Quite a lot of new games work fine on it, just running Far Cry 5 through my 3440x1440, stunningly good. Fallout 4 is good through it. The reason you get the black bars and problems is not the monitor, its the developers. Then lock height to width, so height is a percentage of width. Even if you set the res correctly, you get a messed up menu system. Here is what I had for F4 when I played through:
Edit Fallout4Prefs.ini
Set
iSize W=3440
iSize H=1440

You will need this mod - otherwise the menus are all off the screen:
https://www.nexusmods.com/fallout4/mods/274

And FlawlessWidescreen from:
https://www.flawlesswidescreen.org/

Instructions are in the mod, pretty easy, Flawless widescreen works on other games as well.

With that tweak F4 works fine on widescreen.