There are more reasons other than it is realistic, for having the AI actually use their binoculars and zoom-optics to confirm their targets.
If I was part of one element over-watching another, I had my binoculars on the enemy who is at a extreme distance. My friends in the other element move down the ridge we are on. While watching the enemy, I notice they start reacting suspiciously in the direction of the moving element. I could warn my friends to, "Get down!" There would be a given window of a few seconds it takes for the AI to decide to equip their own binoculars or zoom-optics. This would feel more immersive than the current design.
And realistically as human beings, sometimes we make mistakes of disregarding something in our vision as not being important and continue our business. If the player is wearing camouflage, (Which almost all soldiers in Arma 3 do) positioned in a environment where his camouflage is best suited, and within foliage to assist. He should be able to deceive enemies into thinking he is part of the landscape.