I think that’s appropriate, in that I think the current macOS/Safari/WebKit behavior is clearly a bug: the system should not use the iGPU for WebGL when the dGPU is being used for the monitors, as it clearly leads to bad performance; and I would expect it to use more power overall.
I wonder if you should put a browser detection banner on ThreeJS examples “Hey, we see you are using Safari verion X thru Y which has a bug… you may see worse performance” ?