I have no idea why this increase in firepower didn't play a part in different tactics or doctrine aside from turret fighters and such.
This is where the inflexibility in ADGB/Fighter Command was demonstrated. The old air fighting tactics were retained long after there was a necessity for them. Eventually change was enforced from the bottom (meaning senior men who were actually flying and fighting) up.
It still seems incredible that inexperienced squadrons were rotated into 11 Group, still using the old tactics and formations, even after more experienced units had dispensed with them, but it happened and got a lot of young men killed.
The tactics dated back to at least 1933 when two methods for destroying bomber formations were supposed effective.
1. Sporadic close-in attack
2. Sustained lie-off attack
The first would be carried out typically by single seat interceptors and led to the fighting tactics I posted earlier. These tactics were described in 1933 as 'fire shock action' whatever that was supposed to mean.
The second led to the idea of turret fighters similar multi seat 'no allowance' style fighters and even a single seat fighter with 'extra heavy fore armament'. This was a dead end, but who could have known it in 1933? In a completely different form it is pretty much standard today.
I would just point out that the notion that fighters would need much heavier armament, numbers of machine guns or even cannon, had been around for some time. The 1 1/2 pounder (37mm) COW gun (Coventry Ordnance Works) was specified in the late 1920s for several aircraft projects, Westlands had installed one in an aircraft in 1927.
The entry of Wing Commander Thomson of the Armaments Branch was shortlisted in the Novel Fighter Competition of 1932 and had eight machine guns, though a twin engine pusher biplane. Thomson's argument was that one fighter with many guns was as effective as several with fewer was perceptive.
It was an argument accepted in essence by senior officers most responsible for the procurement of fighters in the late twenties and early thirties (Trenchard, Newall, Higgins) and it is why by the late thirties the eight gun fighter had become standard. Others deserve some credit, but not always as much as they later claimed (Sorley and even Dowding for example).
Cheers
Steve