I agree that for the time, 8 lmg was about as good as it got, but if you can shoot and only 2 of your 8 guns will actually strike a twin engine sized aircraft at 200-300 yards, then why carry 8? If you can shoot, then all 8 should be concentrated, if you only need 2 to take down a plane then remove the other 6 like the KI43.Because pre war / early war when bombers didn't have armour or self sealing tanks any hit from a 303 was to be taken seriously, so increasing the chances of hitting the aircraft had some logic. When protection increased then the need to concentrate the fire became far more important.
Most nations exaggerated the effectiveness of their weapons remembering again that in 1939/40 8 x LMG was far more than the average fighter carried
As I have said, I am not picking on the British, I recall reading that Richard Bong said he had little gunnery training and had to get close to hit them. He went on leave got some gunnery training and said he was a lot better shot after that and would have gotten more kills if he would have had gunnery training at the beginning