Using external data in a composite model and using imported data into measures

Hi all,

I have recently switched to a DirectQuery model within my organization and am trying to use it using also custom data (from an excel file), thus creating a mixed (or composite) model.

Doing so, it creates limited relationships between both data sets, meaning I am unable to use the imported data in measures or calculated columns, be it using RELATED(), LOOKUPVALUE() or any other formula I tried.

I have read plenty of online articles explaining why that is so, but I do not understand how i can therefore use this imported data for calculation purposes.  Is a composite model only good for visualization? If so, imported models are much more convenient as it is possible to use multiple datasources...