I think it is a myth that it is "okay to render blurry frames" for an animation, no one will see the detail.

Yes they will. It tells in the overall.

The lowest I ever set the shade rate is .21, as I was told that 0.0 makes no improvement over .21 but still takes more time. I did not test that.

I will give voice to a completely different strategy. Render with low settings, perhaps even with shadows off, but take it into After Effects and create a highly stylized look. Lack of sharpness and shadows may not matter in that case.

::::: Opera :::::