Agree. Your threat model does not require staying in a cave, but it is worth mentioning what level of paranoia Microsoft or Apple put into devices. Famous Xeno Kovah designed the security of M1 - you may have a sense of LegbaCore amount and quality of contribution to the research community. Microsoft with Surface Pro 4 is IMO is also very interesting because it leverages D-RTM and pushing Secured-core program forward. How this relates to Purism, System76, Framework, and other companies? Those companies will have to follow trends to keep up. The key difference with mentioned giants is that they can provide seamless integration and leverage advanced features for business profit.
Finally, OSS security solutions are not so seamless, but as a community, we should support Qubes and others to improve user experience, so there would be no “inside cave” feeling.
You are right; it is interesting. I read this, and Purism reasoning is clear for me. Please note information from Qubes about firmware and hardware changes during the certification process.
Full disclosure I’m 3mdeb Founder and co-organizer of Qubes OS mini-summit. I know the community pretty well: Purism developers, Insurgo and NitroKey. It is hard to believe that Purism volume (compared to Insurgo and NitroKey) does not allow afford Qubes OS certification. My take on that is that they have different business goals, and that’s why they do not certify - money is just an excuse.