I wonder if the issue is Tesla switching from resistant heating to a combination AC/Heat Pump unit.
On a regular car, heat is provided by hot engine coolant, and the AC will run when in Defrost mode to remove moisture from the heated air. Thus you can have both heat and AC on at the same time.
With a combination AC/heat Pump, you run the compressor in one direction for air conditioning, and run it backwards for heating.
The advantage is that a Heat Pump is more efficient in providing heat than resistance heating, so you get the same heat with less battery drain.
The drawback is that you cannot dry out the heated air with a Heat Pump by using the AC. The pump can't run both directions at the same time.
Also great pumps don’t do well in super cold environments, so they’ll need a resistance heater for at least Canada in any case.
Heat pumps sound like a stupid idea on cars in cold climates. You need a backup resistance heater below maybe 20F.