This talk hurts to watch.

All the block diagrams prominently putting systemd-logind between X11/Wayland-compositor are very misleading, and seems likely to create more misinformed ire for systemd.

systemd-logind is basically just an arbiter of the seats for reasons like you can only have one drm-master on a given drm device at a time. It's not involved in all X11/Wayland-compositor<->kernel interactions. Once the seat has been acquired it gets out of the way. That should not be some huge box right in the middle of the two.

You can trivially confirm this by stracing systemd-logind on your system while interacting with your desktop. It's just sitting idle in epoll_wait().