More from General Mattis here

I will take issue with the following though,
Future enemies will avoid U.S. technological strengths in sensing and targeting, which is the whole idea behind hybrid threats: an enemy that will rapidly shift its posture and adapt its operations and tactics to keep U.S. forces off balance. “Hybrid means you’re going to see a mix of conventional and unconventional… it’s not going to be in four quadrants of a DOD chart with disruptive, catastrophic, traditional and non-traditional war,” Mattis said.
OK, Hybrid Threats is a USMC construct, and I am dead set against it, because it is forcing mechanism for getting the USMC to think, just like Manoeuvre Warfare and 4GW. Forcing mechanisms are bad, because they forgive stupidity and dishonesty. IMO, they have no place in an evolved military.

What he says about the four quadrants of a DOD chart is absolutely correct, and always has been, but that does not make Hybrid the answer.