So, as you have seen, there isn’t really a field matching option for this during import (I have sent a note to our product team to see if this is something that could be put on the radar to add), but there is a way to bulk assign to categories, after import.
If you head to your product page, you will notice that there are checkboxes next to all the products. If you select a batch of products that need to go into a specific category / sub cat, there will be ab action button at the top right of the list of products (You may need to scroll to the right in your browser to see it)
From here, there is an action to mass update the selected products, and in this screen, there is an option to choose the category / sub cat that the selected products should be updated into.
This is a little bit better option than going into each individual product to assign, especially if you have a number of products that need to go into the came cat/sub cat.