The majority of ArmA2 players have to resort to editing their ArmA profile file by hand, in order to set the game difficulty; adjusting the AI accuracy separately from the AI skill level. (See http://community.bistudio.com/wiki/ArmA:_Difficulty). Currently ArmA3 players will have to resort to the same solution.
The ability to adjust accuracy separately from other AI skill levels is important to allow players to adjust the game experience to their liking. The existing single-value "skill" setting provided on the Difficulty options page is insufficient, as I will try to explain below.
I believe that the majority of players like to have the AI "Intelligence" set to a fairly high level so that the AI acts intelligently and presents a tactical challenge. They then control the game difficulty just through adjustment of the AI "Accuracy" setting. Less accurate AI makes for greater fun and easier missions. More accurate AI means more challenge and difficulty.
Having a single slider that affects both accuracy and skill at the same time has an undesirably exponential effect, and makes it difficult to find an acceptable setting. The AI is either dumb and inaccurate - presenting no challenge, or it is smart and deadly - making them unrealisticly super-powered. Adjust the accuracy to an acceptable level, and they are too dumb. Make them smart enough to be challenging, and they are inhumanly accurate.
The most desirable solution would be to have separate difficulty settings for SKILL and ACCURACY for each side (friendly and enemy).
If only one setting per side is possible (as is the case now), then that setting should affect just ACCURACY. SKILL could be pre-set to 'reasonable' values based on testing. Players could still edit their profile if they felt the need to adjust SKILL, but I suspect the majority would not need to; adjusting ACCURACY would be sufficient.
A third AI factor - their sensory acuity - is also a factor that can affect gameplay. If you were going to add a UI control for ACCURACY, then adding one for SENSORY ACUITY would also be beneficial.