rebooted. /usr/bin/wineserver is a symlink to /usr/bin/wineserver-staging-2.16. My superuser only has a couple paths in the $PATH variable, but my regular user has the following:
$echo $PATH /usr/x86_64-pc-linux-gnu/gcc-bin/6.3.0:/usr/lib/llvm/5/bin:/usr/lib/llvm/4/bin:/usr/local/bin:/usr/bin:/bin:/opt/bin:/usr/games/bin:/home/user/usr/lib64/qt5/bin
(that last one is an error in a PATH variable I set up in .bashrc, which I have now corrected).
I don’t see anywhere in that path where another wineserver could be hiding. Does the launcher do anything itself to set the wineserver prefix?