Yeah that one bit is one thing I never understood.
Let's repeat that: Overusing a play means that there's a greater chance, that the play won't be successful.
I get that the defense should "learn to read" the play better, if you're overusing it. But how does your own players get worse at the play? That makes no sense.
Imo, both sides should get "slightly" better when using/facing a play more than 5(?) times per game or something like that. The offense should get better at executing the play and the defense should get better at reading what's happening, as they experienced it.
What could be done, imo, is the defense gets a bigger advantage than the offense, so it in essence works out like it is now; that overuse leads to greater risk of turnovers and failed plays -- but it has to be because the defense adapts and "improves", not because your wide open RB all of a sudden drops a hand off.