As discussed before I think that fliers are way out of balance (for some races more than other). It is something I would love to have adressed for gold (or next gold version) as gold is the netpic version used most widely (IMO).
I did some calculations of AA vs. fliers and it is quite horrifying how terrible AA is compared to the fliers. Please be aware of the numbers shown dont reflect the order of fire, distance, position etc. This is just heads up shooting.
For the calculation I choose to field 1200 points of AA vs 1200 points of fliers. For AA I picked eldar firestorm (which I believe is good AA option compared to others avaliable). For the fliers I picked fliers from different races (also to compare the strength of fliers for myself). I have picked the strongest fliers of the races shown.
The reason for 1200 is that is gives a round number of detachments for all the chosen fliers (and avoids decimals of fliers which would only confuse, even if the math is the same - so 1200 is only for ease of reading).
First I saw how many firestorms each flier would kill if they focused all their fire on the firestorms (pretend everything is visible and in range). All barages with range is assumed to cover only 1 model and barages with no range is disregarded (harridan has bombs that are disregarded). Ork bomber would also kill 1 of its own due to misfire but that has been taken into account. Also remember fliers get additional -1 TSM for "shoot the thin part":
If the firestorms fire back they hit all fliers equally well and would be able to kill a number of fliers depending on the save of each type of flier (and wounds+regenreration for harridan):
The stats are somewhat sad. Fliers are much more dangerous that AA even though AA is supposed to be a specific counter to fliers. Heads up the fliers would win that shooting match if evenly matched for points. The points of firestorms killed per point of flier killed (a cost ratio which reflects the ratio between their effectiveness to eleminate each other) is also abysmal:
Harridans 10,7
Ork Bombers 4,4
Marauder Destroyer 3,1
Eldar Vampire 1,9
Those numbers (especially the Harridan) shows that the stats vs. cost for fliers and AA are not in balance. They should be less than 1 if AA is superior to fliers in heads up shooting.
That said I know the argument will be that positioning is important and I argree, but fliers are easier to position than AA. Plus fliers benefit from -25 cm to enemy fire on top of that.
Next argument is that AA is on first fire so will shoot first and then kill fliers before they can shoot back. That is true, if the flier choose to move into the AA bubble. Still the kill ratio is so high the fliers will still win.
The harridan stats are terrifying with how hard they are to kill and their weapons (disregarding their bombs, infiltration, transport, synapse and hivemind cards).
I think that AA should outshoot fliers point for point. AA is something picked to counter fliers whereas flier weapons can affect everything equally.
P.S. I choose firestorm because I play eldar, but it is not a complaint about firestorms, but rather the imbalance between fliers and AA.