What you're saying makes it sound like the damage model favors aircraft that rely on a high rof over those that rely on high lethality per round when it comes to awarding kills.
I wouldn't say that.... I'd say it's easier to kill with 30mm than .50 cal. Think of all the components that aren't modelled in AH... Control surface lines/linkages, hydraulic lines etc etc. All of that stuff cannot be damaged by .50 cal fire, so you have to make sure that you put your rounds onto parts that will make plane crash quickly.
The damage model favours who ever gets the highest sum of damage first, that's all.
There are no assists if you get in first with the 30mm.
I know it's annoying to see a plane splinter into pieces from your well placed 30mm round only to get an assist for your trouble but look at it as the straw that broke the camels back...