I'll disagree with you there, respectfully. Baseball coaches can put a fielder in the right position to make a play pre-pitch, just like football DC's can use formations to match up correctly. Baseball coaches can tell a hitter that he needs to watch out for an offspeed pitch on a 1-2 count because the pitcher has one to waste, and to lay off of it unless it's perfect...which I know sounds like common sense, but sometimes you've got to remind baseball players because patience can pay off in an at-bat, and they forget that in the heat of the moment sometimes. Righty-lefty matchups, timing your pinch hitters/runners correctly, etc...they have a major bearing on the game.
And that includes preparation and motivation. Drilling the guys in fielding practice so they cut down on errors, working curveballs in batting practice to hitters who are bad at hitting them, engendering an atmosphere of being loose/fun when you need to, and being strict/focus-driven when you need to...it's a delicate balance.
If your premise was right, we wouldn't need a staff at all. Just let the guys show up and play w/o any kind of preparation/planning, and we'd be horrible to watch.