The only "problem" Debian had was that dpkg maintainer had differing opinions on how the merge should have been done and used dpkg as a vessel to express those opinions. Merged /usr was already available in stretch, is the default since buster, and support for non-merged /usr has been dropped in bookworm (all non-merged systems are converted on upgrade now).

Works fine. Debian 12:

    lrwxrwxrwx 1 root root 7 04-28 23:21 bin -> usr/bin
    lrwxrwxrwx 1 root root 7 04-28 23:21 lib -> usr/lib
    lrwxrwxrwx 1 root root 8 04-28 23:21 sbin -> usr/sbin

that on install that was installed somewhere in 2007 then just dist-upgraded for 16 years.