The damage tracking doesn't seem to be effective at reducing the computational cost. Measurement:

Opening https://nh2.me/low-fps-spinners/smooth-spinner.html it doesn't matter if I zoom the spinner to 25% or 500%: Despite the 400x difference in pixels redrawn, the "GPU Process" CPU usage in the "Browser" tab of the Chromium Shift+Esc task manager is equally high.

It only scales down the cost when reducing the FPS.

I am also mystified at how far things have fallen.