The simple answer is that you can detect wheel slip, then you lock slipping wheels with the brakes.
There are a few other systems (not 25k), using a clutch or independent motors, but it doesn't matter: the claimed deficiencies of some AWD only needs to be debunked and corrected.
Watch the linked YouTube video for more details on Subaru's system, the same system cited by the National Park.
Bottom line, a lot of modern AWD systems are perfectly adequate and in some cases superior to 4 wheel drive systems.
There are a few other systems (not 25k), using a clutch or independent motors, but it doesn't matter: the claimed deficiencies of some AWD only needs to be debunked and corrected.
Watch the linked YouTube video for more details on Subaru's system, the same system cited by the National Park.
Bottom line, a lot of modern AWD systems are perfectly adequate and in some cases superior to 4 wheel drive systems.