xorg-server does do more things than wlroots, but it's mostly legacy stuff. In terms of features anyone wants from a modern display server, they're pretty close. wlroots is repsonsible for spinning up an EGL context, talking to libinput, configuring DRM and KMS display resources, allocating GPU resources with GBM, negotiating pixel buffers with clients, etc, all things that xorg-server is doing for TinyWM.
https://cgit.freedesktop.org/xorg/
Most modern xorg drivers depend heavily on mesa to do the heavy lifting:
https://cgit.freedesktop.org/mesa
wlroots depends on mesa as well.
xorg-server does do more things than wlroots, but it's mostly legacy stuff. In terms of features anyone wants from a modern display server, they're pretty close. wlroots is repsonsible for spinning up an EGL context, talking to libinput, configuring DRM and KMS display resources, allocating GPU resources with GBM, negotiating pixel buffers with clients, etc, all things that xorg-server is doing for TinyWM.