If the Hispano was a far better gun, any reason the german's didn't steal it from the french or british early in the war? After all they had to develope the mg151 fron scratch.
Read, Strategy for Defeat The Luftwaffe 1933-1945 by Williamson Murray. It is a very dry read but it answers some question why the Germans did things like they did. Some of it was simply because a cretin engine or gun was all that was available to a particular manufacture base on need like the HS-129 using underpowered French engines because they had them.
Some of it was strictly political kind of like when the US Army replaced the Colt 1911 with the Beretta 92 even after it finished 6th of 8 trial weapons. Maybe that is why the Germans did not copy the Hispano. Part of the reason may be because the Luftwaffe was looking to kill four engined bombers with as few hits as possible while the Allies were only looking to kill other single engine fighters.