While far from perfect, I can assure you that a 750-800 grain 50 caliber ball round at 2500 FPS will do a lot of damage to fuel tanks, engines and pilots.
They didn't actually, the .50 cals didn't show any advantage over the .303's when tested against aircraft targets, a 2 second burst will see approx 160 ball, AP and incendiary .303's guided by tracer towards the target, the .50's will give you about 34 cup and core ball rounds, but only if you fly straight and level.
Did you read what I typed? I said make Grumman fix the guns OR replace them with 8 303's.
And while you are retrofitting guns to Wildcats Spitfires and Hurricanes aren't getting constant speed props, armour kits or 20 other more important things. Adding Wildcats to the British arsenal adds nothing to the course.