Some of the things they miss in the post are Cloudflare uses a customised version or Nginx, same with Fastly for Varnish
(don't know about Netlify and ATS)
Out of the box nginx doesn't support HTTP/2 prioritisation so building a CDN with nginx doesn’t mean you're going ti be delivering as good service as Cloudflare
Another major challenge with CDNs is peering and private backhaul, if you're not pushing major traffic then your customers aren't going to get the best peering with other carriers / ISPs…
HTTP/2 prioritization is a lot of hype for a theoretical feature that yields little real world performance. When a client is rendering a page, it knows what it needs in what order to minimize blocking. The server doesn't.
Out of the box nginx doesn't support HTTP/2 prioritisation so building a CDN with nginx doesn’t mean you're going ti be delivering as good service as Cloudflare
Another major challenge with CDNs is peering and private backhaul, if you're not pushing major traffic then your customers aren't going to get the best peering with other carriers / ISPs…