The original question had to be edited down. I think that the individual deployment of soldiers by unit reflected the lack of full vision about the war. The strategists in the Vietnam War legitimately believed that each stage of the escalating the conflict would guarantee success. Rolling thunder, establishment of ground troops, or Westmoreland's plan were all examples of this. The belief with each escalation stage was that such an action would bring about decisive victory. This is where the individual deployment of troops becomes reflective of a myopic vision. Individual deployment was enacted in the belief that each incremental growth would have secured victory.
I would also make the argument that the war's failure and lack of promise inherent in its escalation impacted the deployment of troops. When it became clear through President Johnson's term in office that the war was an unpopular one and that the initial predictions of victory were off, individual deployment became enacted as a means to continue to staff an initiative that had lost favor with the American public. Individual deployment of units had become needed to staff a war with "more cost" and "more loss" than anything else. This is another area where the escalation of troop numbers in the region was guided by a limited scope and vision of the war's progression.