Manually splitting projection queries and reassembling them client side

Question

I have a seemingly horridly complex query that EF core is struggling with. It executes it (with asSplitQuery) but I suspect its not splitting it in a completely sensible way.

In the old days of datasets you would write a projection of your database into each datatable, and then let the dataset manage the relationships between them.

Is there an EF equivalent? (for projected values) or do people actually project EF data into datasets?