Oh no. It's true: The mouse cursor image on Wayland is delayed by one frame. 馃槶
Proof: https://mort.coffee/home/wayland-input-latency/
Great explaination by @lina: https://lobste.rs/s/oxtwre/hard_numbers_wayland_vs_x11_input_latency#c_edq7tn
A failed attempt to fix this in @gnome: https://gitlab.gnome.org/GNOME/mutter/-/merge_requests/4249
It sounds like there is going to be a new kernel API that would allow updating the cursor independently and therefore earlier, but I couldn't find anything about that.