Awareness, Play Recognition, Man Coverage, and Zone coverage (to a lesser degree) have quite the noticeable effect on how a player plays, outside of any other ratings having to do with a player from a physical standpoint.
The sliders effect how effective, or ineffective, certain ratings are (as you basically stated) therefore meaning that they do play part in the realism of the game.
You could say the ratings are the direct influence over the "realism" of Madden, however because the sliders alter the effectiveness of said ratings, then it too is part of the realism equation.
If this were not true, Ike Taylor would be as good as Nnamdi Asomugha or Darrelle Revis, and he's not.
Also, we do have control over how "intelligent" a player plays on the field to some degree because of the aforementioned ratings, and the relevant sliders.
Enough control to fully correct what is obviously a flawed A.I. to begin with? Certainly not. But there is some control there. To say that there is none would be completely incorrect.