There is a shift of materials in mass movements as well as in erosion from one place to the other. So, why can’t both be treated as one and the same? Can there be appreciable erosion without rocks undergoing weathering?
The course or velocity of the agents of denudation decides the area where the eroded materials will be landed. So if the speed is low it may land in the same area or if it is high it lands in a different area.
Rocks are hard formed by minerals so there isn’t a possible of erosion if the rock is not undergoing weathering.