Varnish is not better in any shape or form than nginx for static content. Varnish has one single usecase, php-sites. - For everything else it will just add a layer of complexity that give no gains. And since varnish is essentially built on apache there is some issues with how it handles connections above about 50k/sec - where it gets complicated to configure, something that nginx does not have.
Do you mean built "for" Apache? Because I think it written from scratch.
I wouldn't call it useless, but it's not exactly a CDN, it's missing the "Network" bit. This is just caching. You'd need something like this, but scaled out on multiple locations for it to be a CDN.
Also most of it isn't exactly NetBSD related, the same approach works on anything that runs Varnish and Nginx.
You might want to read this post on the founding of Varnish https://info.varnish-software.com/blog/history-varnish-cache...
And Fastly would certainly disagree that it’s only useful for PHP as they built a whole company based on Varnish
The rest of what you wrote is either wrong, oversimplified, or inaccurate.
Besides those listed I think a plus would be to only have one server listening on priviliged ports (<1024), using the same/similar TLS configuration for both web and mail, etc. Basically having one service be the arbiter of your incoming traffic and its encryption.
Some people also throw dns via DoH/DoT in: https://www.f5.com/company/blog/nginx/using-nginx-as-dot-doh...