A potential max to limit players progression. We all have potential limits.
A coaching staff with training attributes (for different aspects of football).
A training schedule (team and individual)
A work ethic modifier
Mentors in a players position
Injuries or lack of.
All kinds of things can be part of this. Add what you think would be valid.
I would also have both actual and perceived ratings (actual ratings would be hidden). With both coaches and scouting staffs having evaluation ratings. The longer a player is on your team and the better the evaluation ratings the more accurate the perceived ratings would be to the actual ratings.
Do the same kind of thing for rookie drafting. The better your scouting staff the more accurate the perceived ratings are for evaluating draft prospects.
There are all kinds of things one could do to make CFM be more realistic.