> the experience with proprietary versus open source over the past 30 years had driven home the point that closed ecosystems are almost always far worse for security.
Has it? Can you prove it? I've been using computers for almost 40 years. I've seen foss-enthusiasts repeat that claim ad-nauseam, without proof. All they ave is the vague, hand-wavy, "millions of people read the code!!11".
I use both proprietary and foss software. I write both proprietary and foss software. I have not noticed a meaningful difference in security.
Then I think you haven't been paying attention. We regularly see examples of companies attempting to cover up vulnerabilities, attacking security researchers, dragging their feet on fixes, etc. Meanwhile you can easily see for yourself how long it takes various FOSS projects to get patched and often what the attitude of the devs is.
You can also take an aggregate view. Presumably skilled developers working on major projects should be expected to have similar rates of security issues. So compare CVE frequency between various FOSS and closed source projects.