While running water downhill (fluvial processes) is indeed a significant geomorphological agent that shapes landscapes, it is not the main process. The primary sculpting force that shapes landscapes is plate tectonics, which drives the movement and interaction of tectonic plates. Plate tectonics creates mountains, ocean basins, and other major landforms through processes such as continental drift, mountain building, and volcanic activity.

Running water, in the form of rivers and streams, plays a crucial role in shaping landscapes through erosion and deposition. As water flows downhill, it picks up and transports sediments, including sand, silt, and gravel. This process, known as erosion, gradually wears down landscapes and creates landforms such as valleys, canyons, and alluvial fans.

However, the extent and impact of fluvial processes are largely influenced by the underlying geological structures and climatic conditions. In regions with heavy rainfall and steep slopes, running water can be a dominant force in shaping the landscape. In contrast, in arid environments or areas with more resistant rocks, other processes such as wind erosion (in deserts) or glacial erosion (in mountainous regions) may play a more significant role.

Therefore, while running water is a vital agent in shaping landscapes, its influence is moderated by other geological and environmental factors. Plate tectonics remains the primary driver of landscape evolution, creating the fundamental structures that are subsequently modified by various geomorphic processes, including fluvial processes.