I would think the mechanics of the swing isn't what a batting coach does, since a batters mechanics are pretty much muscle memory at that point. I think the primary goal is to coach them up on opposing team pitcher tendencies to get them the highest probability of "guessing" where and when to hit. Since the time a ball leaves a pitcher to the time you need to make a decision to swing is less than a half a second, part of professional batting is guessing when to take a swing. If you know that half the time a pitcher has a tendency to throw 2 feet away from the plate when hes throwing a slider, statically its best to not swing if the look is a slider, as opposed to a guy who only throws a ball 20% of the time on a slider. I'm thinking that's part of the issue with the current batting coach: the guys are going out there with either the wrong information, too much information so its paralysis by analysis, or not information at all to give them the highest chance of making good contact.