I just found some interesting information.
The Breda-SAFAT is generally regarded as the weakest HMG of WW2.
Even in it’s class of “light caliber” HMGs like the Ho-103 and the German MG 131, it stands out for being extraordinary heavy and slow firing, with a mere 700 RPM.
In fact the gun, firing 12.7x81mm ammunition, weighs practically as much as the US M2, which uses more powerful 12.7x99mm ammo.
Turns out the Italian gun has a barrel that’s not only shorter (800mm) but also heavier (4.72kg) compared to the US gun with a longer (914mm) and lighter barrel (4.4kg).
Using the US barrel as reference a 800mm barrel would otherwise weight roughly 3.85kg.
This might be one of the reasons for the relatively low RoF of the gun, having to move a heavier barrel with a less powerful cartridge.
(Reducing the weight of the parts, like on the Japanese Ho-103, increased the RoF naturally.)
At the same time this would give the gun an edge in accuracy.
A big downside of the US .50cal was it’s moddest sustained fire accuracy of 4 mils, reducing the effective range to 400yd (366m).
Not only is the barrel shorter and sturdier, the round is also moving at lower velocity, inducing less vibration than a faster moving bullet out of a longer and lighter barrel.
If we imagine the Breda-SAFAT having a sustained fire accuracy of 3 mils (similiar to the Hispano), this would mean the effective range would increase by 1/3, so 488m.
In a synchornized installation, where the RoF is further reduced, the accuracy might even be higher than a gun firing at it’s maximum possible rate.
So while the gun might be heavy, it probably traded RoF (useful in dogfights) for range (useful for targeting bombers or as defensive turrets).
So it might have been a compromise, sacrificing some capabilties against fighters for being able to accuractly target bombers outside the effective range of rifle caliber defensive guns.
Being built sturdily most likely also increased reliablity, reducing the amounts of mulfunctions while fighting.
If you have some stories about Italian pilots praising the guns accuracy, feel free to share them.