A-1D/E was normally the Sandy escorts for Jolly Greens, and occasional strike mission aircraft.
A-7D/K was normally a strike mission aircraft that occasionally escorted the Jolly Greens.
So, both aircraft had limited capabilities in both missions, and both carried a heavy load of weapons. The A-1 normally carried rockets and guns, the A-7 normally carried bombs and cannons.
Before the end of the Vietnam War, the USAF
retired the few A-1Ds they had and stayed with the later version A-1E.
After the Vietnam War, the A-7D, and later A-7K replaced the A-1Es in all missions.
Later, the USAF
had the compitition between the A-9A and A-10A for a limited strike aircraft, but speicalized in the CAS mission. Both were excellent aircraft in those missions, but the A-10A was scene as being better able to become a Combat SAR escort aircraft. The A-10 was also considered slightly more survivable.
Thus, the Warthog was born. It replaced the A-7D/K (but the A-7K stayed around until the mid 1990s with some ANG units), the remaining A-1Es, the A-37C, the O-2A, and the OV
The rest is history.