The USAAF did not abandon attack aircraft until tests of XA-41, which resembled the AD Skyraider's fatter, uglier sister. They concluded that compared to the P-51, P-47, and P-38 the A-41 could not defend itself nor be used for air superiority. Bombed-up fighters could do just about as good as dedicated attack aircraft and after they dropped their bombs could do air combat. So the "A" designation went away and the USAF found itself in the unfortunate situation of having to scramble to find enough F-51's to do CAS that were already in the theater until a bunch of Mustangs could be referbed and shipped over from the USA.
The Mustang was not at all the best attack aircraft for the mission in Korea but it was all they had. Jets did not have the range or bombload. The USN was much better off with the F4U and AD. The F-47N would have been much better than the F-51 but they had been phased out. P-47's stored at Tinker AFB Ok were sold at prices so cheap that selling the fuel in the airplanes enabled the buyer to pay for them. The F-82 would have been good but all they had were night fighters.
The A-26 replaced the A-20, B-25 and B-26, but in Korea it was used in strike and interdiction roles rather than strafing and CAS, in other words, level bombing and some rockets.
Vietnam finally forced the USAF to realize they needed some "A" airplanes.