The problem I have with this is that I was using a 1600x1200 21" display in 2000, and got used to workflows for it back then.
I am currently running a 16" display at a similar fractional scaled resolution (because Apple stopped understanding DPI after shipping the first LaserWriter, apparently).
Over that time, my eyes have not gotten better to match display DPI, so I'd rather have web sites just adjust the font size so that there are a reasonable number of words per line instead of rendering whitespace.
Non-full-screen windows would make more sense if Apple supported tiling properly, like most Linux WMs and also modern Windows.
MacOS sort of supports tiling in a "program manager shipped it + got promoted" sort of way, but you have to hover over the window manager buttons, which is slower than just manually arranging stuff. If there are any keyboard shortcuts to invoke tiling, or a way to change the WM buttons to not suck, I have not found them.
1600x1200 is still a 4:3 aspect ratio, I think I agree that scaling that makes sense. Full screen really got problematic with 16:9 and 16:10 aspect ratios. That's when the empty gutters in most apps, and especially websites, became really pronounced.
As for tiling in macOS...
You can use the mouse to drag windows into tiled positions. Grab a window and when your cursor hits the side, corner, or top edge of the screen, it will indicate the tiling position, much like AeroSnap on Windows from some years back. You can also hold the Option key while holding the window to get the tiling regions to show up without moving all the way to the edge.
Keyboard shortcuts exist as well. Go to Settings -> Keyboard -> Keyboard Shortcuts... In the dialog that opens, go to Windows. There you can see all the options and customize them if you'd like. Or set shortcuts for things that might not have one yet.
If for some reason dragging the windows around doesn't work, go to Settings -> Desktop & Dock -> the Windows heading. There are toggles to enable or disable dragging to tile, and the Option key trick. You can also turn off the margins on tiled Windows, which you'd probably want to do.
I've never been a big fan of window tiling myself. There was a time when I needed a lot of different windows visible at all times, but that hasn't been the case in a long time. I find tiling makes things too big or small, it's never what I actually want. I drag the window up to the top of the screen to invoke Fill from time to time, but that's about it.