Basically the main use of Siri for me is lighting---it isn't so bad at setting HomeKit lights scenes---and, with recent shortcuts capability increases, hitting external APIs.

The latter point is a bit broader: now that Siri can hit an arbitrary URL via shortcuts, you can really just set your own trigger phrase to do anything that can be automated. You better believe I have a raspberry pi on order which will be running a local webserver...

May as well just give it a try for yourself and see how you get on. I use Siri all the time to build shopping lists, set reminders (including reminders with alerts), etc. I have no problems with it. I also have no problem issuing the exact command parent poster is having trouble with.

Point is, YMMV; just try it for yourself.

We have a HomePod in the kitchen and its (in my experience) pretty flawless. I empty the milk and I just say 'Hey Siri add milk to the groceries list' and she says 'Ok, added to your groceries list'. If I mumble or stutter things can go off the rails. Also inline editing of my statements causes problems (like where you start saying one word and realizing its the wrong word and swapping it mid-sentence)

I also never have issues and, based on the replies, I'm wondering if the Homepod is the difference. It seems like people using the Homepod as a hub have better luck than those just using their phones.