I think this is a false dichotomy. Open hardware with open source software would be more protected simply by being more stress tested and vetted by more people. If you need even more protection you can employ zero-knowledge proofs and other trustless technologies. I have long been dreaming about some kind of hardware/software co-op creating non-enshittifying versions of thermostats, electric kettles, EV chargers, solar inverters, etc, etc. Hackable for people who want it, simply non-rent-seeking for everyone else.
> more stress tested and vetted by more people
Grandma and grandpa aren't reading the source code and certainly not up at a professional level. This is one of the core misconceptions of the "free/libre" formulation of OSS.
The issue here is rarely whether the security features themselves are circumventable. It’s that at some point this turns into trusting users not to give malware apps permissions (whether that’s a dialog, a system wide setting, adding a third-party app store, etc.). Almost no users can usefully evaluate whether a particular bit of digital trust is a good or bad idea, so people will constantly get scammed in practice. If you’re thinking about ZNP as a solution, you’re not trying to solve the actual security problems of normal users.