That is debatable. For one there is the comfort question - obviously better to preheat by the time you get into the car.
Oh, I agree that it would be more comfortable. But as I said, I was talking about "battery demand reduction". For that matter, for the purposes of "battery demand reduction", you shouldn't heat or cool at all.
My main point is that if you are in a situation where you'll be leaving before the battery will be full (without doing any preheating/precooling), then doing the preheating/precooling on L1 will reduce your range somewhat (maybe it is negligible). We know the power available on L1 is less than what the battery charger can use, so it's a zero sum game. And if you start heating/cooling sooner, you'll use more energy for that.
Now on L2 this might not be the case. First, it might be the case that if the battery charger needs 3.3kw, and the HVAC needs 1.5kw, and the EVSE can supply 6.6kw, then in this situation the car can ask for 4.8 kw total. I don't know. Or, if the charge rate slows down as you near full, then once you hit that regime, the system might be able to divert some of the 3.3kw to the heater. This is all speculation.
Of course, if you've charged your battery to full, none of this matters.