I think the path of least resistance is symlinking /usr/bin/ to /bin, but now that I think about it I think I misunderstood GP's suggestion.
GP's idea, as I am now thinking about it it, is that you could basically move everything out of /usr into /, effectively getting rid of /usr.
Symlinking /usr to / seems like a dubious idea (since we'd get weird things like /usr/etc/passwd) but turning all of its top-level directories into symlinks seems like a possibly OK idea.
Looking at my ubuntu installation, /{bin,sbin, lib,lib32,libx32,lib64) are all links to /usr/{...}, which seems backwards to me. I think they should have hoisted everything into / and made /usr/* symlinks for backward compatibility.
macOS still has a traditional BSD style /bin (37 utilities) and /usr/bin (1000+).
(But why is /bin/sleep a 150K executable? maybe it's a fat binary in more ways than one?)
To avoid breaking backward compatibility.