What I miss the most is the true spacial Finder. Copy a file to a floppy disk, add a custom icon and place it at a precise location on a window. Go to a different Mac and insert the drive. All those attributes are honored. Every single time no matter what. Such a simple and powerful model.
(And honestly, while I see the advantages, I'd rather we not have this feature so we can also not have .DS_Store files. .DS_Store files suck.)
There used to be a one to one mapping of folders to windows. The moment you decide 2 windows can show the content of the same folder simultaneously (which has its advantages), you run in these issues. Which is the canonical view that should be preserved?
And yes, we had all that without . DS_Store files.
I'd posit most of us rarely open the same folder in two different windows, which means the icons should behave as expected in all but an uncommon edge case. It has worked in my experience, at least.
But separately, just as a though experiment: when an icon is moved in one window, the placement ought to update in both windows, in real time. Probably wouldn't have been feasible when macOS X was new, but perfectly doable today given modern computing power.