Actually, I was using an Android voice assistant at the time. I think its name was "Jenkins". You could ask or command it quite a few useful things.
Android had made it easy to create voice commands and searches. That's why when Siri came out, there was almost immediately a ton of "Iris" lookalikes on the Play Store.
Amazon doesn't "know everything" about us. It only knows what things we've commanded through the home assistant. Which is usually a song choice, turning on lights, or asking wacky search questions. If it's a sales order, they'd have know it anyway via doing it online.
Now where assistants are really useful, is when they DO know a lot more about us from our other activities, like Google does. I have no problem with e.g. an online assistant knowing where I was on a certain day. Heck, it's not like there's not a ton of witnesses to that already
I never understand this desire for "privacy" when the same people often use Apple Pay which explicitly gives the banks the same info they always had gotten. And their computerized watch over what we buy and where, has far more effect on our lives than Google's computers knowing that say, I hit a bar in the middle of the day. With Google I'd just get bar ads. But using Apple Pay means the bank is gonna wonder if I lost my job.