Why would they need to "create servers" instead of just throwing UDP packets at you like a normal DDOS?
Because throwing UDP packets requires a bandwidth advantage (aside from reflection attacks), whereas application-layer attacks can impose an outsized cost on the victim.
But you said line rate - that's a simple bandwidth exhaustion.
Line rate of sender != line rate of receiver (I am also not GP).
It probably is though. They're probably both 1Gbps Ethernet.
It's a federated network, so even if everyone has symmetrical 1Gbps links you cant throw 1Gbps at all of them at once.