The problem is that Tesla's traction control is very good but it's reactive so it quickly corrects once it feels slippage or fishtailing by turning on the front drive unit. This is because they are trying to keep the car in the most efficient mode by mostly only using the rear drive unit while driving, which can cause fishtailing on snow.Have had the car less than a month and yesterday was the first experience in a very light coating of snow and was not left feeling confident. It goes great but the moment you take your foot off the accelerator I felt the rear end wanting to fish tail - had to really focus on my driving the rest of the ride.
I force it to use both motors by putting it in off-road mode which makes driving behavior much more predictable and stable since it's no longer reactive. I just drove through I-70 in Colorado during a snow storm and it was night and day difference once I turned off-road mode and had no issues.