But it does. The GPU rerenders your entire screen with all its pixels, even if you change only one. The only thing you can do to avoid that is to not ask the GPU to render a frame. For that you need to reduce FPS.
I'm sure that some spinners are horrible and peg the CPU, but unless your machine is older than ~2018 there is something wrong with your setup if spinners (and not intense operations behind them) cause your battery to suffer.
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.