Not every pilot scored ten kills in one sortie
Even the top aces managed only one kill in ten sorties on average. The vast majority of pilots never got kills.
Aerial gunnery shouldn't be too easy. With small caliber weapons you're only poking holes in the plane. You must be able to hit specific points within the plane, such as the pilot, fuel, coolant, and oil lines, etc. Don't expect to shred wings off with rifle-caliber rounds!