but then once you’ve thousands of servers running the same piece of software across the globe deploying updates and features becomes way slower and way harder. You’ve to consider tests, regressions, a way to properly store and sincronize the blocklists across nodes etc…

This is what we're trying to explain to you, this is how DNS works. Those thousands of servers? Recusrive DNS resolvers, ran by Cloudflare. All watching and caching the records from Cloudflare's authoritative nameservers in near real time, because that's how it was designed. You don't need to test for regressions, figure out how to properly store and synchronize the "blocklist" (it's not a blocklist, it's changing a domain record or simply using a CNAME to point to the registrar) or whatever else, because DNS is continuous, and it was designed to do what you're describing, in the 90's.

Yes, if you're updating your infrastructure, you'd want to test. But this isn't that.

Ever ran into an expired domain and thought about how the registrar can just park an expired domain and make it an ad for themselves? That's just them adding a CNAME in their authoritative nameservers, which gets distributed globally. The prior delinquent owner can still be hosting, but because they don't have the authoritative nameserver they can't use the domain anymore.