You cannot compare the Mercedes-Benz GLS with the Toyota Land Cruiser.
The Toyota is a true sport utility vehicle, body-on-frame truck-based, truly off-roadable and built for that type of harsh environment.
The MB, however, is a crossover, a car-based vehicle built for comfort, meant to be driven and used on paved roads as a modern version of the large American station wagon (or minivan). It may have AWD but it is not really meant to be driven often off-road.
Each vehicle has its uses and when used for the type of driving and environment for which it was built, it does its job well; take it out of its comfort zone, however, and it does not do so well.
The Toyota is a true sport utility vehicle, body-on-frame truck-based, truly off-roadable and built for that type of harsh environment.
The MB, however, is a crossover, a car-based vehicle built for comfort, meant to be driven and used on paved roads as a modern version of the large American station wagon (or minivan). It may have AWD but it is not really meant to be driven often off-road.
Each vehicle has its uses and when used for the type of driving and environment for which it was built, it does its job well; take it out of its comfort zone, however, and it does not do so well.