Umm, there is a difference between turret fighters and two-seaters. Two-seaters, such as the Brisfit, were close enough in performance to match most single-seaters, with the benefit of a protected tail. When the Brits first deployed them, they tried to go with the "flying battle-line" concept, staying in formation and using the flexible guns as the primary weapon. It didn't work very well.
Once the Brits let the pilots fly their aircraft as fighters, letting the gunners protect their tails, then the plane became effective.
Turret fighters, with their big, heavy, and clumsy turrets, didn't have the performance to fly as fighters. The whole idea was to, again, make a flying battle-line, cruise up to the enemy bombers, and shoot them down. When the planes had to dog-fight, they couldn't match the performance of enemy fighters.
CD