Granted, that was ~40 years ago and things are different now, but you can see where the roots of the idea trace back to, and the idea probably has some level of relevance even today. As noted in my other comment, on Windows users often opt out of window management entirely by maximizing everything because it's simpler.
> it's hard to pick out your foreground window from 20 other background windows
This is mostly a casualty of two things: first, the flat UI epidemic which stripped contrast from UIs and made active/inactive windows states less distinct from each other and second, the proliferation of web/Electron apps which for the most part do not implement inactive states for controls at all.
If you boot up a Mac running the last non-flat OS version (10.9 Mavericks) and do work on it with entirely native apps, you'll find that the active window is very visibly active and background windows are very visibly inactive.
The other thing I tend to do is to keep the windows I'm actively using peeking out to click on to foreground which sidesteps the issue of command-tab foregrounding all windows.
Vastly better than Windows (unless 11 has decided to fix them), but grouping windows together in a new desktop involves swiping up, clicking the plus to create a new desktop, dragging both windows to the new desktop. Control left/right to move between the desktops, oh that terminal would be useful as well, and find that there is no native shortcut to move windows between desktops.
You absolutely do not need to resize and drag windows around manually to find the one you want!
I’d argue this probably means you have too many windows open. Part of the abstraction for macOS programs is that the program isn’t the window, and vice versa. You can close all of a program’s windows without closing the program itself. This frees you up to close windows willy-nilly and know that you can just open them back up again if you need to. Keep just what you need for the current task-at-hand open on your desktop and close everything else.
Personally, I’ve actually been using Stage Manager, which takes rapid-unitask- switching toward its maximum level. Just one app open on each screen at a time. Other windows hanging out in-sight, but not cluttery. Switching’s just a click away, and of course all the keyboard shortcuts work nicely, too.
Which is what is so bizarre about it. Everything else about Apple is about cleanliness, focus, minimalism, simplicity.
Yet the windowing system is designed so that everything's overlapping, it's hard to pick out your foreground window from 20 other background windows of varying shapes and sizes and positions, and bringing up Expose/Mission Control shows you something like a detective's corkboard as he tries to connect the dots to solve the case of the serial killer.
It's quite jarring when the rest of the Apple aesthetic is clean minimal lines, and then your windows are meant to look like a three-year-old tossed rectangles all over the place and never cleaned up after themselves.