Cost allocation by branch

I think you want to multiply the cost by the fraction of routes in the current context over the total number of routes for that branch.

This should get you close:

Logistics SAP (Cost per route) =
- [Logistics Cost (KSA)]
    * DIVIDE (
        DISTINCTCOUNT ( Region_to_Van_mapping[Route] ),
        CALCULATE (
            DISTINCTCOUNT ( Region_to_Van_mapping[Route] ),
            REMOVEFILTERS ( Region_to_Van_mapping[Route] )
        ),
        0
    )

In your code, DISTINCTCOUNT is just 1 for each of the routes since the route is part of the filter context for those rows (which is why I remove that filter in the denominator for my DAX).