I have also pretty much given up on Siri. After reading this story, though, I tried to set a reminder on my Watch:
- Me (to my Watch): Set a reminder to call Chris at 3 o clock
- Siri: I wasn't able to create your reminder. Sorry about that.
Then I tried on my phone:
- Me (to my iPhone): Set a reminder to call Chris at 3 o clock
- Siri "OK I'll remind you"
It so frustrating when basic functionality like this doesn't work as expected between connected devices

I briefly thought about un-pairing and re-pairing to see if that would make a difference, but my Watch and iPhone are synced correctly, and I get all my notifications & messages to my Watch correctly, so I don't necessarily want to do that as something else will invariably break. And, TBH, I'm just not enthused enough about Siri anymore to try.
I remember when Siri was first introduced and how groundbreaking it seemed at the time. Shame on you, Apple for running this great tech into the ground.