> The difference between two-wheel and all-wheel drive is night and day, compared to the difference between winter and summer tires.

No, this is incorrect. Just try it.

Summer tires are hopeless in freezing temperatures (and are not rated by the manufacturer to be used in such cold), as they become rock hard. As much grip as plastic kids big wheel tires.

Ultimately, what you need the most, is grip. You could have an 8-wheel drive vehicle but if the tires have no grip it will just spin in place.

In the snow by far the biggest advantage comes from true snow tires (not M+S or all season) due to how much grip they'll provide.

A 4x4 is an additional advantage, of course. A 4x4 on snow tires will do better than a 2-wheel drive with snow tires. But a 2-wheel drive on snow tires is infinitely better than a 4x4 on summer tires because if there is no grip, there's no grip.

If you are driving on pure ice then yes, chains or better yet, studs, are the way to go. That is a very rare scenario.

> Chain controls, and really all winter regulations, like snow load factors in buildings and whatnot, are created locally, not by the state.

No, these are state-wide Caltrans rules.