The biggest missing piece in these definitions? The tires. Most cars these days come with a very highway biased tire. These tires will fail very quickly in most conditions found on off road trails, especially those that are designated as 4x4 required. Failure can be as innocuous as limited traction or complete such as a flat tire from a puncture. If you are in a situation where a tire is punctured from lack of durability how do you think that space saver spare (or can of fix-a-flat) is going to help you get out?
The second major issue with AWD systems is often the clutch based systems that are engaged to transfer power ‘from the wheels that slip to the wheels that grip’. When used in demanding conditions these systems can overheat and shutdown. This also applies to brake biasing systems as well (brakes applied to spinning wheels to transfer torque to other wheels). It can be especially challenging for brakes as there is generally not sufficient air flow over the brakes to cool them during slower speed off-road travel.
The second major issue with AWD systems is often the clutch based systems that are engaged to transfer power ‘from the wheels that slip to the wheels that grip’. When used in demanding conditions these systems can overheat and shutdown. This also applies to brake biasing systems as well (brakes applied to spinning wheels to transfer torque to other wheels). It can be especially challenging for brakes as there is generally not sufficient air flow over the brakes to cool them during slower speed off-road travel.