As far as I can tell (as someone in the networking field but not a DDoS or HA expert), the standard for DDoS mitigation is basically "be bigger": too many POPs/

As far as I can tell (as someone in the networking field but not a DDoS or HA expert), the standard for DDoS mitigation is basically "be bigger": too many POPs/routes, too much capacity to eat packets and establish TCP connections, capacity to serve cached responses, etc. such that even a huge attack simply can't exhaust your resources. To even think about classification and filtering means that you're somehow ingesting and processing this stuff; DDoS becomes threatening exactly when you lack the capacity to do that.