What can I say lol.
You are correct, but Read and React also extends to the wrs, well at least the react part does. By now I'm sure you've heard the theory of the pass reaction slider being reversed, i.e. lower slider means quicker reactions, higher slider means delayed reactions. That only applies on cuts by the wr however. So with 0 pass reaction (and other low numbers) the dbs run the receivers' routes almost before they do, whereas higher numbers allow for a realistic amount of time to pass before the db can react to the cut. Too high, and it's unrealistic in the other way of course.
It does a little more than that. It determines what the DBs make a play on. The higher the number, the more you'll see the DB swat or try to intercept the ball. The lower the number, the more complacent they become.