I would not get too worked up about this for two primary reasons.
First, this unit is comprised basically of first responders to deal with a WMD attack, primarily chemical and/or biological (but we can't rule out Nuclear.) Our civilian medical structure is not equipped to deal with these types of incidences on a major scale. Additionally, these types of attacks employ military style weapons and as such, the military is better equipped to deal with it.
Second, regardless of what the role this "Homeland" unit will serve, the President (any President) doesn't really need it. As soon as a major incident occurs, the President (with full legal authority) will declare a State of Emergency and impose Martial law and suspend the Constitution. When that happens, all military units, including the National Guard are at his disposal. The military doesn't really need to "hide" a dedicated unit in the US. The can access any units needed once Martial law is declared.
But is it just a coincidence that we now have an extensive military trained to operate in urban environments?
I really don't think this is an issue. Our military has always trained to operate in urban environments. Most of WWII, once the allies landed in Europe. Korea, not so much. Vietnam, the Tet offensive and the battles in Saigon and Hue. The entire cold war in Europe with the Russians. True, there have been a lot of operations in the last two decades in urban areas, with the exception of Afghanistan, but I don't think it's a secret that there is no military or insurgency that can stand toe to toe with the US Military. The first Gulf war opened the eyes of the world. At the time, Iraq had the 4th largest military in the world. It took a beating like no other force in the history of warfare. Everyone quickly realized how good our men, equipment, training, and technology really was and that the only way to fight any type of conflict was through an insurgency hidden amongst the population with the goal of slowly dragging out the fight until the US public got tired of the war. The US is gonna fight the enemy wherever they are, recently that focus has taken us into urban areas of the world.
USSA-1