Google has replaced the Google Assistant app on Android with Gemini by default
(www.androidauthority.com)
I played with it some more, and it seems like it's just flaky. I could ask it to turn on the living room lights, and it would, but asking it to turn them off got it to inform me that it can't interact with the outside world.
So it's not as bad as it first told me, but it's still not feature parity, and I'm unlikely to use it if it's not reliable.