Agreed. As I see it there are two main design methods for overcoming this issue.

The first is better for 'anonymous' services; require the client to send a packet of the same size as the buffer they want to receive. It's network in-efficient but for small requests better than the delay in setting up an actual session. It eliminates the chance of amplification attacks.

The second is to establish /some/ kind of session. This might be as 'simple' as logging in, or it could just involve a few round trip communications that indicate the client /is/ listening to server replies. That eliminates every DDoS style except for a man in the middle capable amplification vectors; yet if MitM is possible then why bother with DDoS.