I'm not sure that "computing" lead is quite the right term, things happening a little too fast, more in the same category as muscle memory tasks which are developed via practice. USN and USMC pre and wartime pilots were trained quite a bit in deflection shooting, which actually gives you a lot more aircraft to shoot at! Another issue related to sighting and marksmanship was the harmonization of the guns, especially if there were different calibers and dispersion from nose to wings. A very tight harmonization or nose mounted armament favored a good marksman, lesser souls relied on greater dispersion and spray and pray.