Two NS records can still be one failure domain if both addresses live on one path. Anycast is how authority becomes a network instead of a pair of hosts.
Unicast is easy to understand and easy to flood
Resolvers send queries to a specific address. That address has a home. Congestion, maintenance and DDoS all share it.
Anycast announces the same service everywhere
Cloud DNS uses 210+ Anycast servers. Resolvers reach a nearby available path. Records do not change; reachability does.
Features still sit on top
GeoDNS, health checks and one-second TTLs are record policy. They are only useful if the nameservers are reachable. Anycast is that reachability.
You still need two NS names
Registries want more than one nameserver name even when infrastructure is shared. Follow that, then put both on Anycast.
