Hahahahaha
I have had this same issue the aim bot on arma 3 is pretty intense
I make maps myself and no its not the skill level setting ive made 2 missions now with the AI level set too nothing and they still are able to spot you from hundreds of Metres away and through trees, grass and other objects.
Its fucked and they need to do something about it i put almost 500 hours into arma2 OA
and countless hours into their other titles and have not once come across this problem until now....