This is insane how big these things are now: "There have been some reports of a magnitude in the 1.2 Tbps range; at this time we are unable to verify that claim."
I doesn't have to be. An attack can be highly asymmetric such amplification/reflection attack. I am not saying this is what happened in the Dyn case but rather addressing your average comment. Just an example having hosts in the botnet send queries to non-Dyn open resolvers on the internet and in those queries they spoof the source IPs of Dyn DNS servers. Now all of those open resolvers on internet start sending return traffic to Dyn. If in those spoof request they request EDNS0 those responses could be up to 4K. Compare that to the size of query packet and you have a lot leverage.