Read some history. Look at the North African Campaign during WWII and see why today, the Air Force manages CAS the way it does. Many Americans and Allies died learning how not to manage air assets effectively. The Army used to have organic fixed wing air assets and the Germans almost beat the tar out of us because of it. Doctrine has evolved over the years to leverage the unique capabilities of fixed wing air power. You mention the time delay in getting air support by not having organic air assets (air allocated to a ground commander for his exclusive use)--with our communications capabilities, precision weapons, and fast aircraft, there can and usually is ordnance on a target in less time than it took for me to type this paragraph. The Marines need organic air assets because part of their mission is to be there first with only what they've got with them. That's fine if you're storming a beach or island. With an AOR of an entire country (oh, wait--that's two countries, Iraq and Afghanistan) and units scattered all over, do you think that assigning F-16s/F-15Es or A-10s to individual ground commanders is at all feasible? How many F-16s/F-15Es and A-10s do you think we have? How many do you think we have in theater?
I hate to break your bubble but unless the Marines are storming a beach or island, even their normally organic fixed wing air assets are controlled by a JFACC (Joint Force Air Component Commander) and tasked to support ground troops exactly the same way Navy and Air Force air assets are allocated. The Army and Marines have rotor wing CAS that is supposed to fulfill the organic requirements of individual ground commanders in a theater campaign. Those rotorcraft are probably a stone's throw away from the troops they support. The same can't be said for fixed wing. I just hate it when we want to relearn the same lessons over and over again. 24 years, 3 Mos active duty, numerous tours in multiple joint and combined air operations centers.