This is generally wrong. Disconnect your device from the internet, and on most (for sure Siri/Alexa) will still activate if they hear the wake word. They won't activate it they don't. Both companies have basically said that the wake word functionality is hardware blocked, and that's not been disproven.

Second, not all assistants/companies are created equal. For example, Apple has made the process of involving human review opt-in. Apple also has no incentive to use this data for anything other than improving Siri. They're not an advertising company and if anything are fairly hostile to others using Apple customer's data for that type of thing without explicit consent. Contrary to Alexa/Google, which has an incentive to use your Voice recordings to advertise to you, EG: you ask your VA what the symptoms of food borne illness are, they show an ad or suggest a search for pepto.

And the reality is your phone absolutely does 110% spy on you. Just not by listening to you. It is easy to understand why so many people refuse to believe their voice assistants are not spying on them.

This part is mostly correct. Again, in the case of Apple the phone isn't spying on you, but all of the shit you put on it is. All of those apps are collecting data and collating it in ways that people don't understand. So even though I have a burner Facebook account, since it's tied to my number or email (can't remember which) and I'm sure most of my social graph shares contacts with everything that asks, as soon as I created that account FB suggests to me a whole lot of people I actually know even though I gave it no other real data. People also don't realize that all of this data is often brokered through lots of services, so when you slow down buying tampons or something, another shopping app starts suggesting prenatal vitamins. This is a large part of the reason lots of major retailers have club cards or whatever.