Descobriu que o estilo do Debian funciona perfeitamente. Após o comando acima, isso resolve a situação:
apt-get remove --purge --auto-remove systemd systemd:i386 -y
echo -e 'Package: systemd\nPin: release *\nPin-Priority: -1' > /etc/apt/preferences.d/systemd
echo -e '\n\nPackage: *systemd*\nPin: release *\nPin-Priority: -1' >> /etc/apt/preferences.d/systemd
echo -e '\nPackage: systemd:amd64\nPin: release *\nPin-Priority: -1' >> /etc/apt/preferences.d/systemd
echo -e '\nPackage: systemd:i386\nPin: release *\nPin-Priority: -1' >> /etc/apt/preferences.d/systemd