The simple fact of life of cannon v machinegun is quite simply that the increased size of the cannon round allows the incorporation of high explosive charges, complex fuses and incendiary components. Late in the WWII the RAF carried out extensive evaluations of the effectiveness of many different calibres and types of ammunition. The result was that the 20mm Hispano semi-amour piercing incendiary round was by far the most effective round in aerial combat. It was also very good when used for strafing and was quite capable of penetrating the upper armour of the Panzer Mk4.
Subsequently in the Korean war it was established that .5" Browning ammo. used by the F86 Sabre was being deflected by the airflow over the wings and fuselage of the Mig 15 once speeds got up to round Mach .85. It was established that this was largely due to the light weight of the .5 cal. bullets.