Well, they weren't "sniping".
152-160 rounds per second increases the chances of golden BBs over 50 or so projectiles a second even if they are bigger.
Well, that was hyperbole, in case it wasn't clear.
The point remains, fighter armaments were designed around estimates of how many hits it would, on average, take to shoot down an enemy plane. And on average, it took quite a few rifle caliber MG hits to shoot down a plane, hence why they needed a sizeable battery of fast firing guns.
An argument like ".303 was good enough since a hit to the head of the pilot wins the engagement", while superficially true, doesn't explain why LMG's were considered deficient and replaced and/or supplemented as soon as heavier guns were in a usable state. Particularly considering that heavier guns have a smaller probability of a headshot due to fewer guns and lower RoF.