I just held it for around 25 seconds on a Pixel 8 and it did nothing (except for starting the assistant). I think if you hold it even longer then it does some kind of reset, which isn't a clean shutdown.

I don't mind the repurposing of the power button. I prefer it being used for something else, since I don't power it off very often.

The only thing which bothers me a bit in the repurposed state is that the power-off menu includes an emergency button, which is now hidden behind a couple of levels of swiping and clicking. And accessing it from the lock screen again varies among vendors.