I think this has to do with how the DM system works, rather than power of the cannon itself.
The vast majority of kills we score in AH is associated with structural damage. Some may prefer HOs more than the orthodox style of shooting from behind
... but usually we latch behind a target and shoot him from his 6.
Now, for this general purpose the 30mm cannon is truly a one-ping wonder.
When enough damage is registered that certain part will be destroyed. Usually, these parts are directly associated with the plane's structure - wings, tail section, stabilizers.. etc etc. A hit to these parts will immediately drop that plane from the sky. One ping from the 30mm, will kill the enemy plane if it hits a structure-related area.
However, there are other damageable areas in AH. One major areas is the cockpit , the other is the fuel tanks. The third area, which takes up the entire frontal area of the plane, is the engine block.
Hits to the cockpit result wounds to a pilot. A powerful weapon like the 30mm results in a kill usually.
Nobody is sure how the fuel tanks work, but at least from what we can perceive.. - hits to the fuel tanks will cause a leak, or ignite a fire. Or, if the damage is critical and spontaneous enough, it will explode the plane - usually when it hits a large fuel tank inside the main fuselage.
Hits to the wing tanks usually cause the wing to fall off before receiving enough damage to explode it ( <- this is my theory. I've never actually seen an AH plane explode from damage to the wing fuel tanks. )
However, my guess is, that the engine block has no damage equivalent that is powerful enough to destroy the plane entirely - unlike pilot deaths or fuel explosion/ignition.
For a quick comparison, engine blocks of the planes in IL2/FB are very critical areas. Not only does it leak or seize up, but it also ignites in flames, blows up. Also, some types of powerful damage to the frontal area will cause the destruction of the entire block, causing the engine to fall off from the plane.
Compared to that, I don't think I've seen AH engines ever catch fire. The only fires I've seen are those extending from the rear fuselage(probably meaning flames at rear fuel tanks). Nor have I ever seen an AH engine explode.
I could be wrong - but at least my guess is that hits to the frontal of area of the plane results in only two types of damages to the plane - engine seizure and/or oil leak. I don't think there's a damage type powerful enough to destroy the whole plane, when shots are landed to the engine area.
Perhaps that's why 30mm shots landed at the frontal areas of various planes, only causes fuel leaks or engine stoppage. Come to think of it, I've never exploded an enemy plane in a HO when shots land on his engine block. Pilot kills that blow up the plane, I've seen many times.. but shots landed on the engine part never just blows it up.
ps) Perhaps that is also the reason why there are so many HO collisions in AH....! If you don't blow the enemy up with a pilot kill, or snap his wing off... shots landed to the engine block will only stop his engine - thus, he still travels towards you.... and will ultimatley collide, despite the numbers of shots you've landed on him.
