You dismiss the data you recorded because it doesn’t seem to support your hypothysis tgat there is greater lag in wayland, but that’s not really the right approach, and I think it points to a different conclusion.
You recorded a lag of 5 or 6 frames at 90 frames per second in both Xorg and wayland, which suggests that the lag is the same to within 0.011 seconds, and I don’t think that you can say that’s a huge difference. However, what you didn’t test is the acceleration curve on mouse movement. If that curve is different under wayland it could easily feel infuriatingly laggy without actually showing any extra delay on the movement starting or ending.
I’m not sure how you’d accurately test that, a HID device just sending mouse move events wouldn’t do it as wouldn’t mimic you accelerating the mouse from stationary, so wouldn’t exercise the acceleration curve in wayland. You might need a physical device that moves your actual mouse a fixed dustance and then measure the distance the cursor moves on screen. Repeat for different movement speeds and you might have sone useful data.
Nagios. It does depend on what you mean by monitor though. Nagios is good at telling you that “service A on host B” is down" but less useful for looking at things like performance trends. I particularly like being able to setup dependencies between services, so I get the alert for the root cause, and not all of the services that have gone down because of it.