Not true, Sirloin. There were quite many cases when I would think to myself after an engagement "an assist?? Hell, that wasn't no assist!".. I'm sure everybody experienced these sorts of happenings once in a while.
An enemy plane is being chased by lots of friendlies at deck, getting pinged everywhere but seems to be flying ok, you casually drop down from above, (kill stealing? not when the bozos down below can't drop a single plane chased round and round for many minutes!), get a nice lead shot.. Wammo! His wing falls off and he plummets to the ground.
Message: "assist on XXXX"
It's the thing with the AON(all-or-nuthin') damage modelling. It's AON. A plane pings the target like hell and he flies without damage, since the 'hit points' didn't drop enough to indicate some place on the target is destroyed. Another plane comes along, adds a little bit (but a crucial 'little-bit', the important one too many fleck of hay that broke the donkey's back) and it is bust. The system indicates the one who pinged the guy more, rather than the one who landed the critical hit, as the killer.
I think the AON damage modelling is linked with the power of the guns. Since there isn't any ping specific, complicated damage modelling as we would see in other games like IL-2, I think AH compensates it by giving the guns the ability to snap and destroy the plane with fewer rounds average than IL-2.
What I'd like to see is ping-specific damage modelling. In the case where Tac described below, those multiple .50 pings would not be enough to snap a wing, but the overall performance of the target plane, concerning wing-related actions(rolling and stuff), would degrade considerably. In real life, this is indeed a very important hit, but wouldn't count as a 'shot down' if someone else comes along and ends the misery with a accurate shot that finally blows the target's wings off. And, with ping-specific DM, even though the hit factor announces 'damage' to the specific target area, it wouldn't necessarily mean 'total destruction'. The 1~2 ping hits at 800~1000 yards which blows critical areas off encourages spray and pray lamery more than anything else.