Interesting topic.
I guess you have to start with a definition of 'over practicing'. When muscle fatigue starts affecting the mechanics of your shot (or any repetitive motion, for that matter) and you therefore start adjusting to that base muscle memory, then I can see how over practicing can indeed hurt. That would be different than saying that practicing a lot would hurt your muscle memory, again 'over' practicing being the operative phrase. Maybe the definition of 'over practicing' is when you are modifying what you learned (or grooved through muscle memory) to compensate for fatigue.
Interested to hear what others think.
Take care........................................................Tyler