At what temperature would it consume 2000 watts keeping the battery warm? Surely it uses a heat pump, so it is pumping 8000-4000W of heat into the battery pack. That would be a large steady state heat loss!
A heat pump should be able to do a lot better.
Also you're probably only going to get 16 amps of actual draw on a 20 amp circuit.
Yes it is. I don't have a large dataset of exact temp conditions and charging curves (Elon certainly does though, someone go ask him!) I can tell you if the outdoor temps are below 15F a standard outlet has negative net energy input.
A heat pump solution would certainly be more efficient, knowing Tesla I can only assume it's peltier junctions.
All the hype about the efficiency of an EV goes out the window when it's blowing 16kwh+ a day just keeping the battery above freezing.