Regarding the wisdom of having the USAF as a separate service. You do have a valid point that many in the USAF do not give CAS it's proper importance. I am part of an AF TACP unit right now, and we are down and dirty with the Army troops, so trust me, we see the importance, as do many whole communities in the USAF (A-10s, AC-130's, even F-16s). That said, the flip side of that coin is that many in the Army do not realize the importance of the strategic level air campaign, and they often do not realize the importance of absolute air dominance at times.
The classic example was in North Africa in WW2. The Army commanders wanted the air assigned at the lower echelons so that the ground forces could see that they had friendly air supporting them. That ended up being a huge failure in actual practice though, as air power needs to be massed for best effects in a situation like that. What many of the Battalion, Brigade, and even Division level leaders failed to realize, and certainly the grunt on the ground probably wasn't thinking about is that it is far more effective to kill a column of tank via interdiction miles behind the battle area, vs trying to distinguish friend from foe and pick them off once they are deployed in the front line area. This is still true today. Even with all our technology, fratricide is still a huge threat, so it is always better to interdict the enemy in an area where that is not a factor if possible. If you have also taken out the bridges, rail lines, and natural choke-points such as mountain passes, tunnels, etc then even better. We learned that lesson in Korea as well. That does not remove the need for CAS to support your friendlies against the enemies that have already made it to the battle area.
As far as air superiority, if you don't have it, you will lose. Period. There are basically zero instances of a conventional battle being won by a force that did not have at least local air superiority. Everybody sees air superiority and thinks "killing enemy airplanes", but that is only part of it. We have that part licked, as even our F-15C's, which are the most dominant fighter plane in history, are still capable of seizing and holding not just air superiority, but air dominance if enemy planes are all we are talking about. However, air superiority also includes enemy surface-to-air threats, and there are some truly scary ones out there now. These systems are starting to be proliferated to all of our potential enemies, and will render any aircraft useless (or dead) that does not have stealth technology baked in, as well as state of the art electronic countermeasures. Watching the exercises here at GREEN FLAG-West at the NTC, it has been a revelation to me how even a single SA-6 battery (not modern SAM technology by any means) can stiff-arm CAS out of the fight for hours on end before it is finally SEAD'd or DEAD'd.