This was my experience as well. While it is less straining on the eyes, that was the only benefit I saw. I didn't see a reduction in screen time or less anxiety about notifications.

I set grayscale in my phone's quiet hours settings. It's to help me sleep, rather than to reduce my phone usage. It means if I wake in the night and look at my phone, I'm not blasted by colors. Or if I stay up a bit later than usual. I find it beneficial although probably not revolutionary.

I did try setting my phone to grayscale during the day but didn't see much if any benefits there.