Anecdotal data coming in hot.
I use Siri daily for controlling HomeKit devices. She's not always on point though. I've named a light basically "Radiohouse", because that's what the designer called it, but 25% of the time she insists of playing radio instead of turning on the light. I'm not a native english speaker and communicate with Siri in Danish, but still. Siri is definitely not useless and I would love for her to become a lot better.
You may be right that the majority probably doesn't use Siri, but that's because it doesn't really make sense to use Siri on the phone. I rely on HomePod speakers to interface with it, that makes a lot more sense for me.