Or, the lesson is: if you want to prosecute a rapist, don’t bring up rapes other than the one you are prosecuting.
The defense brought this up at trial not because Weinstein had expensive lawyers, but because any competent defense attorney would. At that point, the judge decided the defense was wrong, and the prosecution decided to take the risk that the defense was right. That risk backfired. Now, every Judge, prosecutor, and defense attorney in the juristiction is on notice about how to correctly apply prior bad acts rules to sexual assult cases, so they should be able to avoid making this mistake again.