I wouldn't say this. I just had a bad alternator plaguing for my car for almost 2 years and it was the alternator underperforming and malfunctioning. I had no codes. I would randomly get the Charging System now error but it wouldn't stay on permanently, it would randomly pop up and and go away.Yup, BCM only runs the alternator at the needed duty cycle for the car's electrical demands to save a tiny bit of fuel/wear. If your alternator is actually underperforming it will almost always set a code.
Wasn't until my alternator was really jacked up and it was causing my car to stall and make a loud electrical whining sound that I found out that the alternator was the source of all my problems.
Not saying that you don't know what you are talking about or anything just saying to not rule out the alternator