For those of you who have deprecated sddm because of sddm bug #602 and 612 - unable to focus or Activate window for the primary screen #602 the fix has moved to Sparky for me in lxqt. sddm is still quite slow, especially on an atom with 1Gb.
Coming soon in lightdm (it hit unstable) is a lightdm.conf change that appears to be smoothing the way forward for Wayland. I accepted it. Normally I keep my existing .conf 's in /etc . But, ever onwards toward Wayland, whenever that might be.
peace out.
EDIT Not so minor changes for some for lightdm. I am not affected.
https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=829348