Large scale dns vendors have a multi million dollars worth of network layer traffic filtering equipment pipelined in front of their DNS servers (or in house solutions such as Google).
Does that mean running your own DNS in the cloud is a better answer? This is what I do.
Virtual private cloud services where you host the DNS server may also include DDoS protection.
Yes, of course. But my question was why are you focusing on DNS here? Everything you've said so far is true of setting up literally any public service. Considering how cheap DNS is to serve in the common case, running an authoritative DNS server seems no less risky than running, say, a web server.