I disagree with how you categorize lethality, firing time and ballistics on primary and secondary weapons.
First, I think you're overrating lethality. Yeah, the taters on the 109K pack a nasty punch, but just HITTING with them takes a lot of practice and luck. In a fighter vs. fighter engagement I'd say the 30mm is MAINLY a factor of fear--to the detriment of the K-4 because damned if any fighter who sees him coming is going to give him a clean shot.
For example: the A6M's 20mm cannon have the advantage in hitting power over the .50cal of the F4F, but the Ma Deuce's advantage in ballistics and muzzle velocity make them the FAR more effective weapons package (ok, I'll give you that this is an EW comparison, but the same can be said comparing German and American iron. The cannon on the German fighters may have the raw hitting power advantage, but the US .50cal are much easier to hit with).
For this reason, lethality and ballistics properties should both be weighted together in this case, perhaps one being a multiplier to the other, or averaging them together? Something like:
Gun Package = (Lethality + Ballistics)/2
As for Primary vs. Secondary:
You're SPECIFICALLY considering this as the actual primary and secondary triggers, correct? NOT assuming mixed weapon packages: IE, all cannon on primary and all machine guns as secondary? If this is the case remember the P-40E, P-51s, P-47s, F4F/FM-2, F4Us and F6Fs all have the same type of guns in both primary and secondary banks. In this case, I think the ballistics and firing time of the secondary bank is QUITE significant, considering that all the guns in the planes I mentioned have the same ballistics properties, (Browning .50cal for all except the F4U-1C) as opposed to aircraft with mixed armaments that can have a modest (.50cal and Hispano) to radical (German 13mm + 30mm) variance in the ballistics and muzzle velocity. Not only that, but some of these aircraft have an even distribution of rounds between both gun banks.
For example, if you look at the ammo distribution on the P-51B one pair of guns has 250rds/gun, the other has 380. The FM-2 has 430rds in all four guns. Both carry the Browning .50cal so ballistics don't come into the equation, but the FM-2 has a MAJOR advantage in firing time. Additionally, because the FM-2 distributes ammunition between all four guns equally she has a major advantage in lethality: The P-51B loses half its firepower after firing roughly 2/3 her total firing time. The FM-2's lethality remains consistent right up until the guns go dry.
To accurately rate all weapons on an aircraft we'd be looking at an even more complex equation. Maybe something like:
Gun Package = ( (Primary Lethality + Primary Ballistics + Primary Firing Time) / 3) + (Secondary Lethality + Primary Ballistics + Secondary Firing Time / 3 ) ) / 2