Someone decided that it is wrong to use symlink in /etc/X11/Xsession
My though are that we should allow links to allow for example a user
to link to /dev/null and prevent problem such as disk full because of
bugs in packages (for example remmina which fills the logs with SSL
errors when it freezes).

Even after forcing .Xsession to log to /dev/null, gdm-session-worker
from gdm3 package forces us to log to a file and just don't care about
what you've got to say!
The file MUST be a regular file AND be writable, else it creates one
for you and will try really hard to create a file. There's no way
around.