I do not want a centralized, home assistant that controls and monitors everything unless it is open source software hosted on my own computers that stores data on my own servers, without sending to 3rd parties.
Because complaining about, or refusing to buy, Amazon's or Google's offering, is not furthering your desired outcome. The only way to beat them is to actually make what you describe more useful and user-friendly than what they are offering.
If parent said they really wanted a home assistant, but felt a conflicted due to their desire for it to be open source, they’d have an issue.
Personally I just don’t adopt this tech. I used to be an early adopter but I don’t really need more efficient ways to buy Amazon stuff and the Spotify app already makes a great music remote for my home stereo.
I'm curious about what recording everything in my home, and then seeking legal protections on it as my intellectual property (e.g. copyright) could benefit me. Could I sue spying apps as copyright infringement?
However, voicing my desire for such IS useful, because if enough people voice it, then someone might decide there is a market for it, and build it.
How such a venture could make money, I have no idea. Systems set up and installation, I suppose.