Wigan Warrior
I perhaps mis-led you. The size of Marine Air is roughly comensurate to that of its ground counterpart. That allows for Marines to provide CAS for Marines with some degree of excess but not enough for it to be the primary provider, nor is that the structure in combined operaions. While the US Army may ask and prefer Marine CAS, the USAF provides the lions share to the Army. The air element commander assigns from a pool based on operational considerations and specific mission. For one assignment it might be USMC air supporting Army and for the next it might be USAF for the Marines.