drgondog
Major
Maybe not many of them were developed around 1939 (Ju 88, Pe 2, B 25) but plenty of aircraft were capable of doing the same work in a better way at the same time that the A 20 was in widespread service, such as the Mosquito, the Beaufighter, the fighterbombers (P 38, P 47, P 40, Typhoon, Fw 190, Bf 110), all capable of doing pinpoint bombing and straffing with a sizable bomb load, faster and better air capability.
My point is that the light bomber was largely a compromise in WW2 that wasn't as capable as a medium bomber in payload and range and wasn't able enough to survive unescorted so better the resources were directed in others ways and since the A 20 can be regarded as the epitome of the light bomber, therefore can be judged as overrated.
It wasn't as versatile as other twins, neither exceptionally good at its main role.
The A-20 was spawned when the USAAC became aware that they still were part of the US Army and the Air Ground Support role was evolving to include fast but light and well armed attack bombers to provide tactical air support beyond enemy lines. They AAC evolved their thinking based on observations of the Spanish conflict and the early successes of the LW/Wermacht in Europe.
For that role it was vey successful indeed, and was also a fairly good low to medium altitude light bomber with greater range and load than any US fighter or Allied/Axis fighter (I'm talking air superiority fighter until late 1943) until the Douglas A-26 replaced it. The P-39 and P-40 were substitutes for the Attack fighter role to balance against extremely slow and vulnerable A-24 etc until the AAF decided on the A-36 Mustang, modified for max performance under 5500 feet. By the time the A-36 was operational to team with the A-20, AAF doctrine had matured to point the fighter as a battlefield air superiority role combined with CAS. The Merlin Mustang was originally selected to replace P-39/P-40 but the air war in ETO/MTO took them away from TAC. But remember ONLY the NAA Mustang derivatives and the P-38 were equipped with bomb racks capable of 500/1000 pound GP until the P-47D-15/-16 were produced and delivered ~ March 1944.