I would say Wingmen are usually quite good at attacking other aircraft - (and I release mine to do this quite often) -
However, as for avoiding SAMS - I find the AI of wingmen not to be so great - (I really think Janes completely overlooked the ability to have the option of "rating" your wingmen in the game (be it from Rookie to Ace level) -
You can do this in the "quick mission" but there is no option for this within the regular missions....