The author talked about cursor latency being worse with Wayland, and claimed that it was likely a consequence of the major architectural differences between X11 and Wayland. Is this an inherent drawback of Wayland, or is it just something that's true for one implementation, e.g. GNOME?

It's a implementation issue(or a driver), Wayland don't dictate the mouse latency, and compositors are free todo whatever they want with it

I figured. I'm not sure if the author meant that it was an inherent drawback, but it does seem like he still has a bit of lingering bias towards X11 in his reassessment article.