The significance is that there's less weight on the front wheels and less friction, so they will turn more easily. That all adds up to making it easier for them to start rotating if the rear has lost grip. So what I'm saying is the less weight over the front wheels the worse this situation is likely to be, regardless of how much weight is over the rear wheels.
I'm struggling with the logic of this, TBH.
There are no parking brakes on the front wheels of most cars (the only exception I know of were some older Citroen's that had inboard brakes at the front). Therefore the front wheels will turn pretty much as easily on any car - bearing resistance change with load is so tiny as to be almost unmeasurable.
The biggest factors affecting rolling resistance are the temperature, tyre compound and tread pattern (summer tyres have a fair bit lower rolling resistance that winter tyres). Tyre pressure has an effect, by reducing the area of the contact patch, which in turn reduces the angular deflection of the tyre tread and sidewall as it rotates, but in the case of the Tesla that's compensated for by the increased mass The reason that the tyre pressures are higher on Teslas is to give the same contact patch area despite the higher mass, so the tyre rolling resistance remains pretty much the same as any other car with a similar handling versus efficiency tyre section/load/pressure compromise (which is pretty much every car made in the past 20 years or so).
When parked, the rear wheels will be locked by the parking brake and the front wheels will be as free to rotate as those on any other car. Those on the AWD cars will have a slightly increased front wheel drag because of the front transmission, but for the single motor models the front wheel drag will be the same as for any other rear wheel drive car, and that will be pretty negligible on a surface with a low enough friction coefficient as to allow the locked rear wheels to start sliding.
The only forces acting to stop any parked car from sliding/rolling away will be effectiveness of the parking brakes (and it seems that in the cases quoted they were locking up the rear wheels) and the resistance to sliding resulting from the coefficient of friction between the road surface and the rear tyre contact patches. The front wheels aren't going to contribute any worthwhile resistance, because they are as free to rotate as on any other car, because the contact patch area, determined by the wheel loading and tyre pressure, will be near enough the same.
Looking at other cars, then quite a few have a much lower front wheel loading that even the Model 3 SR+ (which has the lowest front wheel loading of any Tesla, I believe). Perhaps the most extreme example would be rear engined Porsche models, where only around 40% of the weight is over the front wheels, compared with 48% over the front wheels for the Model 3 AWD versions. At the other extreme might be some of the older, front engine, rear wheel drive, cars, that had maybe 55% to 60% of the weight over the front wheels. All seem able to slide down slippery slopes with the rear wheels locked, but if I had to guess I'd say that those most resistant to this would be the models with the highest rearward weight bias. Many years ago I had a beach buggy, built from a 1950's vintage VW Beetle. With the engine hanging out behind the rear wheels, that had a massive rearward weight bias, so very low front wheel loading. It was fantastic on snow, or any slippery ground, because the high rear wheel loading gave the rear wheels loads of grip. I never tested it, but I suspect that high rear wheel grip on slippery surfaces would also have given it a lot of resistance to sliding when parked.
