on one of your points. Catching the ball is just ONE, physical skill that a wr needs. There are a ton of new skills and tricks that a wr needs to learn coming out of high school. Hand placement, how to get away with pushing off a db, coverage recognition and route adjustment, upper body leverage, efficient route running, influencing a db to bite or jump a route, etc. It takes time and a great, experienced teacher to get this done.
One other point for those that don't think position coaches matter. All you have to do is look at USC. They have all the talent in the world but ex-players down here in LA are all over Lynn Swann for the less-than- adequate position coaches there in the past 6 years.